[c#] Is there an easy way to check the .NET Framework version?

The problem is that I need to know if it's version 3.5 SP 1. Environment.Version() only returns 2.0.50727.3053.

I found this solution, but I think it will take much more time than it's worth, so I'm looking for a simpler one. Is it possible?

This question is related to c# .net

The answer is


Something like this should do it. Just grab the value from the registry

For .NET 1-4:

Framework is the highest installed version, SP is the service pack for that version.

RegistryKey installed_versions = Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\NET Framework Setup\NDP");
string[] version_names = installed_versions.GetSubKeyNames();
//version names start with 'v', eg, 'v3.5' which needs to be trimmed off before conversion
double Framework = Convert.ToDouble(version_names[version_names.Length - 1].Remove(0, 1), CultureInfo.InvariantCulture);
int SP = Convert.ToInt32(installed_versions.OpenSubKey(version_names[version_names.Length - 1]).GetValue("SP", 0));

For .NET 4.5+ (from official documentation):

using System;
using Microsoft.Win32;


...


private static void Get45or451FromRegistry()
{
    using (RegistryKey ndpKey = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry32).OpenSubKey("SOFTWARE\\Microsoft\\NET Framework Setup\\NDP\\v4\\Full\\")) {
        int releaseKey = Convert.ToInt32(ndpKey.GetValue("Release"));
        if (true) {
            Console.WriteLine("Version: " + CheckFor45DotVersion(releaseKey));
        }
    }
}


...


// Checking the version using >= will enable forward compatibility,  
// however you should always compile your code on newer versions of 
// the framework to ensure your app works the same. 
private static string CheckFor45DotVersion(int releaseKey)
{
    if (releaseKey >= 461808) {
        return "4.7.2 or later";
    }
    if (releaseKey >= 461308) {
        return "4.7.1 or later";
    }
    if (releaseKey >= 460798) {
        return "4.7 or later";
    }
    if (releaseKey >= 394802) {
        return "4.6.2 or later";
    }
    if (releaseKey >= 394254) {
        return "4.6.1 or later";
    }
    if (releaseKey >= 393295) {
        return "4.6 or later";
    }
    if (releaseKey >= 393273) {
        return "4.6 RC or later";
    }
    if ((releaseKey >= 379893)) {
        return "4.5.2 or later";
    }
    if ((releaseKey >= 378675)) {
        return "4.5.1 or later";
    }
    if ((releaseKey >= 378389)) {
        return "4.5 or later";
    }
    // This line should never execute. A non-null release key should mean 
    // that 4.5 or later is installed. 
    return "No 4.5 or later version detected";
}

I find it easier to work with the Version class:

using Microsoft.Win32;
using System.Runtime.InteropServices;

namespace System.Runtime.InteropServices {
  public static class RuntimeInformationEx {

    public static Version? GetDotnetFrameworkVersion() {
      using var key = Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full");
      if (key is object) {
        if (!Int32.TryParse(key.GetValue("Release", "").ToString(), out var release)) return null;
        return release switch
        {
          378389 => new Version(4, 5, 0),
          378675 => new Version(4, 5, 1),
          378758 => new Version(4, 5, 1),
          379893 => new Version(4, 5, 2),
          393295 => new Version(4, 6, 0),
          393297 => new Version(4, 6, 0),
          394254 => new Version(4, 6, 1),
          394271 => new Version(4, 6, 1),
          394802 => new Version(4, 6, 2),
          394806 => new Version(4, 6, 2),
          460798 => new Version(4, 7, 0),
          460805 => new Version(4, 7, 0),
          461308 => new Version(4, 7, 1),
          461310 => new Version(4, 7, 1),
          461808 => new Version(4, 7, 2),
          461814 => new Version(4, 7, 2),
          528040 => new Version(4, 8, 0),
          528209 => new Version(4, 8, 0),
          528049 => new Version(4, 8, 0),
          _ => null
        };

      } else { // .NET version < 4.5
        using var key1 = Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\NET Framework Setup\NDP");
        if (key1 is null) return null;
        var parts = key1.GetSubKeyNames()[^1].Substring(1).Split('.'); // get lastsub key, remove 'v' prefix, and split
        if (parts.Length == 2) parts = new string[] { parts[0], parts[1], "0" };
        if (parts.Length != 3) return null;
        Func<string, int> Parse = s => Int32.TryParse(s, out var i) ? i : -1;
        try { return new Version(Parse(parts[0]), Parse(parts[1]), Parse(parts[2])); } catch { return null; }
      }
    }

    public static Version? GetDotnetCoreVersion() {
      if (!RuntimeInformation.FrameworkDescription.StartsWith(".NET Core ")) return null;
      var parts = RuntimeInformation.FrameworkDescription.Substring(10).Split('.');
      if (parts.Length == 2) parts = new string[] { parts[0], parts[1], "0" };
      if (parts.Length != 3) return null;
      Func<string, int> Parse = s => Int32.TryParse(s, out var i) ? i : -1;
      try { return new Version(Parse(parts[0]), Parse(parts[1]), Parse(parts[2])); } catch { return null; }
    }
  }
}

(code is C#8)


Little large, but looks like it is up-to-date to Microsoft oddities:

    public static class Versions
    {
        static Version 
            _NET;

        static SortedList<String,Version>
            _NETInstalled;

#if NET40
#else
        public static bool VersionTry(String S, out Version V)
        {
            try
            { 
                V=new Version(S); 
                return true;
            }
            catch
            {
                V=null;
                return false;
            }
        }
#endif
        const string _NetFrameWorkKey = "SOFTWARE\\Microsoft\\NET Framework Setup\\NDP";
        static void FillNetInstalled()
        {
            if (_NETInstalled == null)
            {
                _NETInstalled = new SortedList<String, Version>(StringComparer.InvariantCultureIgnoreCase);
                RegistryKey
                    frmks = Registry.LocalMachine.OpenSubKey(_NetFrameWorkKey);
                string[]
                    names = frmks.GetSubKeyNames();
                foreach (string name in names)
                {
                    if (name.StartsWith("v", StringComparison.InvariantCultureIgnoreCase) && name.Length > 1)
                    {
                        string
                            f, vs;
                        Version
                            v;
                        vs = name.Substring(1);
                        if (vs.IndexOf('.') < 0)
                            vs += ".0";
#if NET40
                        if (Version.TryParse(vs, out v))
#else
                        if (VersionTry(vs, out v))
#endif
                        {
                            f = String.Format("{0}.{1}", v.Major, v.Minor);
#if NET40
                            if (Version.TryParse((string)frmks.OpenSubKey(name).GetValue("Version"), out v))
#else
                            if (VersionTry((string)frmks.OpenSubKey(name).GetValue("Version"), out v))
#endif
                            {
                                if (!_NETInstalled.ContainsKey(f) || v.CompareTo(_NETInstalled[f]) > 0)
                                    _NETInstalled[f] = v;
                            }
                            else
                            { // parse variants
                                Version
                                    best = null;
                                if (_NETInstalled.ContainsKey(f))
                                    best = _NETInstalled[f];
                                string[]
                                    varieties = frmks.OpenSubKey(name).GetSubKeyNames();
                                foreach (string variety in varieties)
#if NET40
                                    if (Version.TryParse((string)frmks.OpenSubKey(name + '\\' + variety).GetValue("Version"), out v))
#else
                                    if (VersionTry((string)frmks.OpenSubKey(name + '\\' + variety).GetValue("Version"), out v))
#endif
                                    {
                                        if (best == null || v.CompareTo(best) > 0)
                                        {
                                            _NETInstalled[f] = v;
                                            best = v;
                                        }
                                        vs = f + '.' + variety;
                                        if (!_NETInstalled.ContainsKey(vs) || v.CompareTo(_NETInstalled[vs]) > 0)
                                            _NETInstalled[vs] = v;
                                    }
                            }
                        }
                    }
                }
            }
        } // static void FillNetInstalled()

        public static Version NETInstalled
        {
            get
            {
                FillNetInstalled();
                return _NETInstalled[_NETInstalled.Keys[_NETInstalled.Count-1]];
            }
        } // NETInstalled

        public static Version NET
        {
            get
            {
                FillNetInstalled();
                string
                    clr = String.Format("{0}.{1}", Environment.Version.Major, Environment.Version.Minor);
                Version
                    found = _NETInstalled[_NETInstalled.Keys[_NETInstalled.Count-1]];
                if(_NETInstalled.ContainsKey(clr))
                    return _NETInstalled[clr];

                for (int i = _NETInstalled.Count - 1; i >= 0; i--)
                    if (_NETInstalled.Keys[i].CompareTo(clr) < 0)
                        return found;
                    else
                        found = _NETInstalled[_NETInstalled.Keys[i]];
                return found;
            }
        } // NET
    }

public class DA {
  public static class VersionNetFramework {
    public static string Get45or451FromRegistry()
    {//https://msdn.microsoft.com/en-us/library/hh925568(v=vs.110).aspx
        using (RegistryKey ndpKey = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry32).OpenSubKey("SOFTWARE\\Microsoft\\NET Framework Setup\\NDP\\v4\\Full\\"))
        {
            int releaseKey = Convert.ToInt32(ndpKey.GetValue("Release"));
            if (true)
            {
                return (@"Version: " + CheckFor45DotVersion(releaseKey));
            }
        }
    }
    // Checking the version using >= will enable forward compatibility, 
    // however you should always compile your code on newer versions of
    // the framework to ensure your app works the same.
    private static string CheckFor45DotVersion(int releaseKey)
    {//https://msdn.microsoft.com/en-us/library/hh925568(v=vs.110).aspx
        if (releaseKey >= 394271)
            return "4.6.1 installed on all other Windows OS versions or later";
        if (releaseKey >= 394254)
            return "4.6.1 installed on Windows 10 or later";
        if (releaseKey >= 393297)
            return "4.6 installed on all other Windows OS versions or later";
        if (releaseKey >= 393295)
            return "4.6 installed with Windows 10 or later";
        if (releaseKey >= 379893)
            return "4.5.2 or later";
        if (releaseKey >= 378758)
            return "4.5.1 installed on Windows 8, Windows 7 SP1, or Windows Vista SP2 or later";
        if (releaseKey >= 378675)
            return "4.5.1 installed with Windows 8.1 or later";
        if (releaseKey >= 378389)
            return "4.5 or later";

        return "No 4.5 or later version detected";
    }
    public static string GetVersionFromRegistry()
    {//https://msdn.microsoft.com/en-us/library/hh925568(v=vs.110).aspx
        string res = @"";
        // Opens the registry key for the .NET Framework entry.
        using (RegistryKey ndpKey =
            RegistryKey.OpenRemoteBaseKey(RegistryHive.LocalMachine, "").
            OpenSubKey(@"SOFTWARE\Microsoft\NET Framework Setup\NDP\"))
        {
            // As an alternative, if you know the computers you will query are running .NET Framework 4.5 
            // or later, you can use:
            // using (RegistryKey ndpKey = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, 
            // RegistryView.Registry32).OpenSubKey(@"SOFTWARE\Microsoft\NET Framework Setup\NDP\"))
            foreach (string versionKeyName in ndpKey.GetSubKeyNames())
            {
                if (versionKeyName.StartsWith("v"))
                {

                    RegistryKey versionKey = ndpKey.OpenSubKey(versionKeyName);
                    string name = (string)versionKey.GetValue("Version", "");
                    string sp = versionKey.GetValue("SP", "").ToString();
                    string install = versionKey.GetValue("Install", "").ToString();
                    if (install == "") //no install info, must be later.
                        res += (versionKeyName + "  " + name) + Environment.NewLine;
                    else
                    {
                        if (sp != "" && install == "1")
                        {
                            res += (versionKeyName + "  " + name + "  SP" + sp) + Environment.NewLine;
                        }

                    }
                    if (name != "")
                    {
                        continue;
                    }
                    foreach (string subKeyName in versionKey.GetSubKeyNames())
                    {
                        RegistryKey subKey = versionKey.OpenSubKey(subKeyName);
                        name = (string)subKey.GetValue("Version", "");
                        if (name != "")
                            sp = subKey.GetValue("SP", "").ToString();
                        install = subKey.GetValue("Install", "").ToString();
                        if (install == "") //no install info, must be later.
                            res += (versionKeyName + "  " + name) + Environment.NewLine;
                        else
                        {
                            if (sp != "" && install == "1")
                            {
                                res += ("  " + subKeyName + "  " + name + "  SP" + sp) + Environment.NewLine;
                            }
                            else if (install == "1")
                            {
                                res += ("  " + subKeyName + "  " + name) + Environment.NewLine;
                            }
                        }
                    }
                }
            }
        }
        return res;
    }
    public static string GetUpdateHistory()
    {//https://msdn.microsoft.com/en-us/library/hh925567(v=vs.110).aspx
        string res=@"";
        using (RegistryKey baseKey = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry32).OpenSubKey(@"SOFTWARE\Microsoft\Updates"))
        {
            foreach (string baseKeyName in baseKey.GetSubKeyNames())
            {
                if (baseKeyName.Contains(".NET Framework") || baseKeyName.StartsWith("KB") || baseKeyName.Contains(".NETFramework"))
                {

                    using (RegistryKey updateKey = baseKey.OpenSubKey(baseKeyName))
                    {
                        string name = (string)updateKey.GetValue("PackageName", "");
                        res += baseKeyName + "  " + name + Environment.NewLine;
                        foreach (string kbKeyName in updateKey.GetSubKeyNames())
                        {
                            using (RegistryKey kbKey = updateKey.OpenSubKey(kbKeyName))
                            {
                                name = (string)kbKey.GetValue("PackageName", "");
                                res += ("  " + kbKeyName + "  " + name) + Environment.NewLine;

                                if (kbKey.SubKeyCount > 0)
                                {
                                    foreach (string sbKeyName in kbKey.GetSubKeyNames())
                                    {
                                        using (RegistryKey sbSubKey = kbKey.OpenSubKey(sbKeyName))
                                        {
                                            name = (string)sbSubKey.GetValue("PackageName", "");
                                            if (name == "")
                                                name = (string)sbSubKey.GetValue("Description", "");
                                            res += ("    " + sbKeyName + "  " + name) + Environment.NewLine;
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
        return res;
    }
}

using class DA.VersionNetFramework

private void Form1_Shown(object sender, EventArgs e)
{
    //
    // Current OS Information
    //
    richTextBox1.Text = @"Current OS Information:";
    richTextBox1.AppendText(Environment.NewLine +
                            "Machine Name: " + Environment.MachineName);
    richTextBox1.AppendText(Environment.NewLine +
                            "Platform: " + Environment.OSVersion.Platform.ToString());
    richTextBox1.AppendText(Environment.NewLine +
                            Environment.OSVersion);
    //
    // .NET Framework Environment Information
    //
    richTextBox1.AppendText(Environment.NewLine + Environment.NewLine +
                                       ".NET Framework Environment Information:");
    richTextBox1.AppendText(Environment.NewLine +
                            "Environment.Version " + Environment.Version);
    richTextBox1.AppendText(Environment.NewLine + 
                            DA.VersionNetFramework.GetVersionDicription());
    //
    // .NET Framework Information From Registry
    //
    richTextBox1.AppendText(Environment.NewLine + Environment.NewLine +
                                       ".NET Framework Information From Registry:");
    richTextBox1.AppendText(Environment.NewLine +
                            DA.VersionNetFramework.GetVersionFromRegistry());
    //
    // .NET Framework 4.5 or later Information From Registry
    //
    richTextBox1.AppendText(Environment.NewLine + 
                                       ".NET Framework 4.5 or later Information From Registry:");
    richTextBox1.AppendText(Environment.NewLine +
                            DA.VersionNetFramework.Get45or451FromRegistry());
    //
    // Update History
    //
    richTextBox1.AppendText(Environment.NewLine + Environment.NewLine +
                            "Update History");
    richTextBox1.AppendText(Environment.NewLine + 
                            DA.VersionNetFramework.GetUpdateHistory());
    //
    // Setting Cursor to first character of textbox
    //
    if (!richTextBox1.Text.Equals(""))
    {
        richTextBox1.SelectionStart = 1;
    }
}

Result:

Current OS Information: Machine Name: D1 Platform: Win32NT Microsoft Windows NT 6.2.9200.0

.NET Framework Environment Information: Environment.Version 4.0.30319.42000 .NET 4.6 on Windows 8.1 64 - bit or later

.NET Framework Information From Registry: v2.0.50727 2.0.50727.4927 SP2 v3.0 3.0.30729.4926 SP2 v3.5 3.5.30729.4926 SP1

v4
Client 4.6.00079 Full 4.6.00079 v4.0
Client 4.0.0.0

.NET Framework 4.5 or later Information From Registry: Version: 4.6 installed with Windows 10 or later

Update History Microsoft .NET Framework 4 Client Profile
KB2468871
KB2468871v2
KB2478063
KB2533523
KB2544514
KB2600211
KB2600217
Microsoft .NET Framework 4 Extended
KB2468871
KB2468871v2
KB2478063
KB2533523
KB2544514
KB2600211
KB2600217
Microsoft .NET Framework 4 Multi-Targeting Pack
KB2504637 Update for (KB2504637)


An alternative method where no right to access the registry are needed, is to check for the existence of classes that are introduced in specific framework updates.

private static bool Is46Installed()
{
    // API changes in 4.6: https://github.com/Microsoft/dotnet/blob/master/releases/net46/dotnet46-api-changes.md
    return Type.GetType("System.AppContext, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089", false) != null;
}

private static bool Is461Installed()
{
    // API changes in 4.6.1: https://github.com/Microsoft/dotnet/blob/master/releases/net461/dotnet461-api-changes.md
    return Type.GetType("System.Data.SqlClient.SqlColumnEncryptionCngProvider, System.Data, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089", false) != null;
}

private static bool Is462Installed()
{
    // API changes in 4.6.2: https://github.com/Microsoft/dotnet/blob/master/releases/net462/dotnet462-api-changes.md
    return Type.GetType("System.Security.Cryptography.AesCng, System.Core, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089", false) != null;
}

private static bool Is47Installed()
{
    // API changes in 4.7: https://github.com/Microsoft/dotnet/blob/master/releases/net47/dotnet47-api-changes.md
    return Type.GetType("System.Web.Caching.CacheInsertOptions, System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a", false) != null;
}

You can get a useful string without having to touch the registry or reference assemblies which may or may not be loaded. mscorlib.dll and other System assemblies have AssemblyFileVersionAttribute defined, and it seems to be unique for each version of .NET, based on the reference assemblies provided with Visual Studio.

string version = (typeof(string).Assembly
    .GetCustomAttributes(typeof(AssemblyFileVersionAttribute), false)
    .FirstOrDefault() as AssemblyFileVersionAttribute)?.Version;

Version 4.5 is a bit off, because it's marked 4.0 in that version, but 4.6 onward appear to have the minor version matching at least. Doing it this way seems like it would be more future proof than depending on some installer registry key and having to compare against a fixed set of values.

I found the reference assemblies here:

C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework

Where I got the following versions:

4.0 = 4.0.30319.1
4.5 = 4.0.30319.18020
4.5.1 = 4.0.30319.18402
4.5.2 = 4.0.30319.34211
4.6 = 4.6.81.0
4.6.1 = 4.6.1055.0
4.7.2 = 4.7.3062.0
4.8 = 4.8.3761.0

Environment.Version() is giving the correct answer for a different question. The same version of the CLR is used in .NET 2.0, 3, and 3.5. I suppose you could check the GAC for libraries that were added in each of those subsequent releases.


Thank you for this post which was quite useful. I had to tweak it a little in order to check for framework 2.0 because the registry key cannot be converted straightaway to a double. Here is the code:

string[] version_names = rk.GetSubKeyNames();
//version names start with 'v', eg, 'v3.5'
//we also need to take care of strings like v2.0.50727...
string sCurrent = version_names[version_names.Length - 1].Remove(0, 1);
if (sCurrent.LastIndexOf(".") > 1)
{
    string[] sSplit = sCurrent.Split('.');
    sCurrent = sSplit[0] + "." + sSplit[1] + sSplit[2];
}
double dCurrent = Convert.ToDouble(sCurrent, System.Globalization.CultureInfo.InvariantCulture);
double dExpected = Convert.ToDouble(sExpectedVersion);
if (dCurrent >= dExpected)

It used to be easy, but Microsoft decided to make a breaking change: Before version 4.5, each version of .NET resided in its own directory below C:\Windows\Microsoft.NET\Framework (subdirectories v1.0.3705, v1.1.4322, v2.0.50727, v3.0, v3.5 and v4.0.30319).

Since version 4.5 this has been changed: Each version of .NET (i.e. 4.5.x, 4.6.x, 4.7.x, 4.8.x, ...) is being installed in the same subdirectory v4.0.30319 - so you are no longer able to check the installed .NET version by looking into Microsoft.NET\Framework.

To check the .NET version, Microsoft has provided two different sample scripts depending on the .NET version that is being checked, but I don't like having two different C# scripts for this. So I tried to combine them into one, here's the script GetDotNetVersion.cs I created (and updated it for 4.7.1 framework):

using System;
using Microsoft.Win32;
public class GetDotNetVersion
{
    public static void Main(string[] args)
    {
        Console.WriteLine((args != null && args.Length > 0) 
                          ? "Command line arguments: " + string.Join(",", args) 
                          : "");

        string maxDotNetVersion = GetVersionFromRegistry();
        if (String.Compare(maxDotNetVersion, "4.5") >= 0)
        {
            string v45Plus = GetDotNetVersion.Get45PlusFromRegistry();
            if (v45Plus != "") maxDotNetVersion = v45Plus;
        }
        Console.WriteLine("*** Maximum .NET version number found is: " + maxDotNetVersion + "***");
    }

    private static string Get45PlusFromRegistry()
    {
        String dotNetVersion = "";
        const string subkey = @"SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full\";
        using (RegistryKey ndpKey = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry32).OpenSubKey(subkey))
        {
            if (ndpKey != null && ndpKey.GetValue("Release") != null)
            {
                dotNetVersion = CheckFor45PlusVersion((int)ndpKey.GetValue("Release"));
                Console.WriteLine(".NET Framework Version: " + dotNetVersion);
            }
            else
            {
                Console.WriteLine(".NET Framework Version 4.5 or later is not detected.");
            }
        }
        return dotNetVersion;
    }

    // Checking the version using >= will enable forward compatibility.
    private static string CheckFor45PlusVersion(int releaseKey)
    {
        if (releaseKey >= 528040) return "4.8 or later";
        if (releaseKey >= 461808) return "4.7.2";
        if (releaseKey >= 461308) return "4.7.1";
        if (releaseKey >= 460798) return "4.7";
        if (releaseKey >= 394802) return "4.6.2";
        if (releaseKey >= 394254) return "4.6.1";
        if (releaseKey >= 393295) return "4.6";
        if ((releaseKey >= 379893)) return "4.5.2";
        if ((releaseKey >= 378675)) return "4.5.1";
        if ((releaseKey >= 378389)) return "4.5";

        // This code should never execute. A non-null release key should mean
        // that 4.5 or later is installed.
        return "No 4.5 or later version detected";
    }

    private static string GetVersionFromRegistry()
    {
        String maxDotNetVersion = "";
        // Opens the registry key for the .NET Framework entry.
        using (RegistryKey ndpKey = RegistryKey.OpenRemoteBaseKey(RegistryHive.LocalMachine, "")
                                        .OpenSubKey(@"SOFTWARE\Microsoft\NET Framework Setup\NDP\"))
        {
            // As an alternative, if you know the computers you will query are running .NET Framework 4.5 
            // or later, you can use:
            // using (RegistryKey ndpKey = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, 
            // RegistryView.Registry32).OpenSubKey(@"SOFTWARE\Microsoft\NET Framework Setup\NDP\"))
            foreach (string versionKeyName in ndpKey.GetSubKeyNames())
            {
                if (versionKeyName.StartsWith("v"))
                {
                    RegistryKey versionKey = ndpKey.OpenSubKey(versionKeyName);
                    string name = (string)versionKey.GetValue("Version", "");
                    string sp = versionKey.GetValue("SP", "").ToString();
                    string install = versionKey.GetValue("Install", "").ToString();
                    if (install == "") //no install info, must be later.
                    {
                        Console.WriteLine(versionKeyName + "  " + name);
                        if (String.Compare(maxDotNetVersion, name) < 0) maxDotNetVersion = name;
                    }
                    else
                    {
                        if (sp != "" && install == "1")
                        {
                            Console.WriteLine(versionKeyName + "  " + name + "  SP" + sp);
                            if (String.Compare(maxDotNetVersion, name) < 0) maxDotNetVersion = name;
                        }

                    }
                    if (name != "")
                    {
                        continue;
                    }
                    foreach (string subKeyName in versionKey.GetSubKeyNames())
                    {
                        RegistryKey subKey = versionKey.OpenSubKey(subKeyName);
                        name = (string)subKey.GetValue("Version", "");
                        if (name != "")
                        {
                            sp = subKey.GetValue("SP", "").ToString();
                        }
                        install = subKey.GetValue("Install", "").ToString();
                        if (install == "")
                        {
                            //no install info, must be later.
                            Console.WriteLine(versionKeyName + "  " + name);
                            if (String.Compare(maxDotNetVersion, name) < 0) maxDotNetVersion = name;
                        }
                        else
                        {
                            if (sp != "" && install == "1")
                            {
                                Console.WriteLine("  " + subKeyName + "  " + name + "  SP" + sp);
                                if (String.Compare(maxDotNetVersion, name) < 0) maxDotNetVersion = name;
                            }
                            else if (install == "1")
                            {
                                Console.WriteLine("  " + subKeyName + "  " + name);
                                if (String.Compare(maxDotNetVersion, name) < 0) maxDotNetVersion = name;
                            } // if
                        } // if
                    } // for
                } // if
            } // foreach
        } // using
        return maxDotNetVersion;
    }
    
} // class

On my machine it outputs:

v2.0.50727 2.0.50727.4927 SP2
v3.0 3.0.30729.4926 SP2
v3.5 3.5.30729.4926 SP1
v4
Client 4.7.03056
Full 4.7.03056
v4.0
Client 4.0.0.0
.NET Framework Version: 4.7.2 or later
**** Maximum .NET version number found is: 4.7.2 or later ****

The only thing that needs to be maintained over time is the build number once a .NET version greater than 4.7.1 comes out - that can be done easily by modifying the function CheckFor45PlusVersion, you need to know the release key for the new version then you can add it. For example:

if (releaseKey >= 461308) return "4.7.1 or later";

This release key is still the latest one and valid for the Fall Creators update of Windows 10. If you're still running other (older) Windows versions, there is another one as per this documentation from Microsoft:

.NET Framework 4.7.1 installed on all other Windows OS versions 461310

So, if you need that as well, you'll have to add

if (releaseKey >= 461310) return "4.7.1 or later";

to the top of the function CheckFor45PlusVersion. Likewise it works for newer versions. For example, I have added the check for 4.8 recently. You can find those build numbers usually at Microsoft.


Note: You don't need Visual Studio to be installed, not even PowerShell - you can use csc.exe to compile and run the script above, which I have described here.


Update: The question is about the .NET Framework, for the sake of completeness I'd like to mention how to query the version of .NET Core as well - compared with the above, that is easy: Open a command shell and type:

dotnet --info Enter

and it will list the .NET Core version number, the Windows version and the versions of each related runtime DLL as well. Sample output:

.NET Core SDK (reflecting any global.json):
  Version: 2.1.300
  Commit: adab45bf0c

Runtime Environment:
  OS Name: Windows
  OS Version: 10.0.15063
  OS Platform: Windows
  RID: win10-x64
  Base Path: C:\Program Files\dotnet\sdk\2.1.300


Host (useful for support):
  Version: 2.1.0
  Commit: caa7b7e2ba

.NET Core SDKs installed:
  1.1.9 [C:\Program Files\dotnet\sdk]
  2.1.102 [C:\Program Files\dotnet\sdk]
  ...
  2.1.300 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.0 [C:\Program
  Files\dotnet\shared\Microsoft.AspNetCore.All]
  ...
  Microsoft.NETCore.App 2.1.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]

To install additional .NET Core runtimes or SDKs:
  https://aka.ms/dotnet-download

Note that

  • if you only need the version number without all the additional information, you can use
    dotnet --version.

  • on a 64 bit Windows PC, it is possible to install the x86 version side by side with the x64 version of .NET Core. If that is the case, you will only get the version that comes first in the environment variable PATH. That is especially important if you need to keep it up to date and want to know each version. To query both versions, use:

C:\Program Files\dotnet\dotnet.exe --version
3.0.100-preview6-012264
C:\Program Files (x86)\dotnet\dotnet.exe --version
3.0.100-preview6-012264

In the example above, both are the same, but if you forgot to update both instances, you might get different results! Note that Program Files is for the 64bit version, and Program Files (x86) is the 32bit version.


Update: If you prefer to keep the build numbers in a list rather than in a cascade of if-statements (as Microsoft suggested), then you can use this code for CheckFor45PlusVersion instead:

private static string CheckFor45PlusVersion(int releaseKey)
{
    var release = new Dictionary<int, string>()
    {
            { 378389, "4.5" },
            { 378675, "4.5.1" }, { 379893, "4.5.2" },
            { 393295, "4.6" },
            { 394254, "4.6.1" }, { 394802, "4.6.2" },
            { 460798, "4.7" },
            { 461308, "4.7.1" }, { 461808, "4.7.2" },
            { 528040, "4.8 or later" }
    };
    int result = -1;
    foreach(var k in release.OrderBy(k=>k.Key))
    {
        if (k.Key <= releaseKey) result = k.Key; else break;
    };
    return (result > 0) ? release[result] : "No 4.5 or later version detected";
}

Update with .NET 4.6.2. Check Release value in the same registry as in previous responses:

RegistryKey registry_key = Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full");
if (registry_key == null)
    return false;
var val = registry_key.GetValue("Release", 0);
UInt32 Release = Convert.ToUInt32(val);

if (Release >= 394806) // 4.6.2 installed on all other Windows (different than Windows 10)
                return true;
if (Release >= 394802) // 4.6.2 installed on Windows 10 or later
                return true;

AFAIK there's no built in method in the framework that will allow you to do this. You could check this post for a suggestion on determining framework version by reading windows registry values.


I have changed Matt's class so it can be reused in any project without printing all its checks on Console and returning a simple string with correct max version installed.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.Win32;

namespace MyNamespace
{
    public class DotNetVersion
    {
        protected bool printVerification;

        public DotNetVersion(){
            this.printVerification=false;
        }
        public DotNetVersion(bool printVerification){
            this.printVerification=printVerification;
        }


        public string getDotNetVersion(){
            string maxDotNetVersion = getVersionFromRegistry();
            if(String.Compare(maxDotNetVersion, "4.5") >= 0){
                string v45Plus = get45PlusFromRegistry();
                if(!string.IsNullOrWhiteSpace(v45Plus)) maxDotNetVersion = v45Plus;
            }
            log("*** Maximum .NET version number found is: " + maxDotNetVersion + "***");

            return maxDotNetVersion;
        }

        protected string get45PlusFromRegistry(){
            String dotNetVersion = "";
            const string subkey = @"SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full\";
            using(RegistryKey ndpKey = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry32).OpenSubKey(subkey)){
                if(ndpKey != null && ndpKey.GetValue("Release") != null){
                    dotNetVersion = checkFor45PlusVersion((int)ndpKey.GetValue("Release"));
                    log(".NET Framework Version: " + dotNetVersion);
                }else{
                    log(".NET Framework Version 4.5 or later is not detected.");
                }
            }
            return dotNetVersion;
        }

        // Checking the version using >= will enable forward compatibility.
        protected string checkFor45PlusVersion(int releaseKey){
            if(releaseKey >= 461308) return "4.7.1 or later";
            if(releaseKey >= 460798) return "4.7";
            if(releaseKey >= 394802) return "4.6.2";
            if(releaseKey >= 394254) return "4.6.1";
            if(releaseKey >= 393295) return "4.6";
            if((releaseKey >= 379893)) return "4.5.2";
            if((releaseKey >= 378675)) return "4.5.1";
            if((releaseKey >= 378389)) return "4.5";

            // This code should never execute. A non-null release key should mean
            // that 4.5 or later is installed.
            log("No 4.5 or later version detected");
            return "";
        }

        protected string getVersionFromRegistry(){
            String maxDotNetVersion = "";
            // Opens the registry key for the .NET Framework entry.
            using(RegistryKey ndpKey = RegistryKey.OpenRemoteBaseKey(RegistryHive.LocalMachine, "")
                                            .OpenSubKey(@"SOFTWARE\Microsoft\NET Framework Setup\NDP\")){
                // As an alternative, if you know the computers you will query are running .NET Framework 4.5 
                // or later, you can use:
                // using(RegistryKey ndpKey = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, 
                // RegistryView.Registry32).OpenSubKey(@"SOFTWARE\Microsoft\NET Framework Setup\NDP\"))
                string[] subKeyNnames = ndpKey.GetSubKeyNames();
                foreach(string versionKeyName in subKeyNnames){
                    if(versionKeyName.StartsWith("v")){
                        RegistryKey versionKey = ndpKey.OpenSubKey(versionKeyName);
                        string name =(string)versionKey.GetValue("Version", "");
                        string sp = versionKey.GetValue("SP", "").ToString();
                        string install = versionKey.GetValue("Install", "").ToString();
                        if(string.IsNullOrWhiteSpace(install)){ //no install info, must be later.
                            log(versionKeyName + "  " + name);
                            if(String.Compare(maxDotNetVersion, name) < 0) maxDotNetVersion = name;
                        }else{
                            if(!string.IsNullOrWhiteSpace(sp) && "1".Equals(install)){
                                log(versionKeyName + "  " + name + "  SP" + sp);
                                if(String.Compare(maxDotNetVersion, name) < 0) maxDotNetVersion = name;
                            }

                        }
                        if(!string.IsNullOrWhiteSpace(name)){
                            continue;
                        }

                        string[] subKeyNames = versionKey.GetSubKeyNames();
                        foreach(string subKeyName in subKeyNames){
                            RegistryKey subKey = versionKey.OpenSubKey(subKeyName);
                            name =(string)subKey.GetValue("Version", "");
                            if(!string.IsNullOrWhiteSpace(name)){
                                sp = subKey.GetValue("SP", "").ToString();
                            }
                            install = subKey.GetValue("Install", "").ToString();
                            if(string.IsNullOrWhiteSpace(install)){
                                //no install info, must be later.
                                log(versionKeyName + "  " + name);
                                if(String.Compare(maxDotNetVersion, name) < 0) maxDotNetVersion = name;
                            }else{
                                if(!string.IsNullOrWhiteSpace(sp) && "1".Equals(install)){
                                    log("  " + subKeyName + "  " + name + "  SP" + sp);
                                    if(String.Compare(maxDotNetVersion, name) < 0) maxDotNetVersion = name;
                                }
                                else if("1".Equals(install)){
                                    log("  " + subKeyName + "  " + name);
                                    if(String.Compare(maxDotNetVersion, name) < 0) maxDotNetVersion = name;
                                } // if
                            } // if
                        } // for
                    } // if
                } // foreach
            } // using
            return maxDotNetVersion;
        }

        protected void log(string message){
            if(printVerification) Console.WriteLine(message);
        }

    } // class
}

If your machine is connected to the internet, going to smallestdotnet, downloading and executing the .NET Checker is probably the easiest way.

If you need the actual method to deterine the version look at its source on github, esp. the Constants.cs which will help you for .net 4.5 and later, where the Revision part is the relvant one:

                           { int.MinValue, "4.5" },
                           { 378389, "4.5" },
                           { 378675, "4.5.1" },
                           { 378758, "4.5.1" },
                           { 379893, "4.5.2" },
                           { 381029, "4.6 Preview" },
                           { 393273, "4.6 RC1" },
                           { 393292, "4.6 RC2" },
                           { 393295, "4.6" },
                           { 393297, "4.6" },
                           { 394254, "4.6.1" },
                           { 394271, "4.6.1" },
                           { 394747, "4.6.2 Preview" },
                           { 394748, "4.6.2 Preview" },
                           { 394757, "4.6.2 Preview" },
                           { 394802, "4.6.2" },
                           { 394806, "4.6.2" },

As of version 4.5 Microsoft changed the way it stores the .NET Framework indicator in the registry. There official guidance on how to retrieve the .NET framework and the CLR versions can be found here: https://msdn.microsoft.com/en-us/library/hh925568(v=vs.110).aspx

I am including modified version of their code to address the bounty question of how you determine the .NET framework for 4.5 and higher here:

using System;
using System.Reflection;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Microsoft.Win32;

namespace stackoverflowtesting
{
    class Program
    {
        static void Main(string[] args)
        {
            Dictionary<int, String> mappings = new Dictionary<int, string>();

            mappings[378389] = "4.5";
            mappings[378675] = "4.5.1 on Windows 8.1";
            mappings[378758] = "4.5.1 on Windows 8, Windows 7 SP1, and Vista";
            mappings[379893] = "4.5.2";
            mappings[393295] = "4.6 on Windows 10";
            mappings[393297] = "4.6 on Windows not 10";

            using (RegistryKey ndpKey = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry32).OpenSubKey("SOFTWARE\\Microsoft\\NET Framework Setup\\NDP\\v4\\Full\\"))
            {
                int releaseKey = Convert.ToInt32(ndpKey.GetValue("Release"));
                if (true)
                {
                    Console.WriteLine("Version: " + mappings[releaseKey]);
                }
            }
            int a = Console.Read();
        }
    }
}

public class DA
{
    public static class VersionNetFramework
    {
        public static string GetVersion()
        {
            return Environment.Version.ToString();
        }
        public static string GetVersionDicription()
        {
            int Major = Environment.Version.Major;
            int Minor = Environment.Version.Minor;
            int Build = Environment.Version.Build;
            int Revision = Environment.Version.Revision;

            //http://dzaebel.net/NetVersionen.htm
            //http://stackoverflow.com/questions/12971881/how-to-reliably-detect-the-actual-net-4-5-version-installed

            //4.0.30319.42000 = .NET 4.6 on Windows 8.1 64 - bit
            if ((Major >=4) && (Minor >=0) && (Build >= 30319) && (Revision >= 42000))
                return @".NET 4.6 on Windows 8.1 64 - bit or later";
            //4.0.30319.34209 = .NET 4.5.2 on Windows 8.1 64 - bit
            if ((Major >= 4) && (Minor >= 0) && (Build >= 30319) && (Revision >= 34209))
                return @".NET 4.5.2 on Windows 8.1 64 - bit or later";
            //4.0.30319.34209 = .NET 4.5.2 on Windows 7 SP1 64 - bit
            if ((Major >= 4) && (Minor >= 0) && (Build >= 30319) && (Revision >= 34209))
                return @".NET 4.5.2 on Windows 7 SP1 64 - bit or later";
            //4.0.30319.34014 = .NET 4.5.1 on Windows 8.1 64 - bit
            if ((Major >= 4) && (Minor >= 0) && (Build >= 30319) && (Revision >= 34014))
                return @".NET 4.5.1 on Windows 8.1 64 - bit or later";
            //4.0.30319.18444 = .NET 4.5.1 on Windows 7 SP1 64 - bit(with MS14 - 009 security update)
            if ((Major >= 4) && (Minor >= 0) && (Build >= 30319) && (Revision >= 18444))
                return @".NET 4.5.1 on Windows 7 SP1 64 - bit(with MS14 - 009 security update) or later";
            //4.0.30319.18408 = .NET 4.5.1 on Windows 7 SP1 64 - bit
            if ((Major >= 4) && (Minor >= 0) && (Build >= 30319) && (Revision >= 18408))
                return @".NET 4.5.1 on Windows 7 SP1 64 - bit or later";
            //4.0.30319.18063 = .NET 4.5 on Windows 7 SP1 64 - bit(with MS14 - 009 security update)
            if ((Major >= 4) && (Minor >= 0) && (Build >= 30319) && (Revision >= 18063))
                return @".NET 4.5 on Windows 7 SP1 64 - bit(with MS14 - 009 security update) or later";
            //4.0.30319.18052 = .NET 4.5 on Windows 7 SP1 64 - bit
            if ((Major >= 4) && (Minor >= 0) && (Build >= 30319) && (Revision >= 18052))
                return @".NET 4.5 on Windows 7 SP1 64 - bit or later";
            //4.0.30319.18010 = .NET 4.5 on Windows 8
            if ((Major >= 4) && (Minor >= 0) && (Build >= 30319) && (Revision >= 18010))
                return @".NET 4.5 on Windows 8 or later";
            //4.0.30319.17929 = .NET 4.5 RTM
            if ((Major >= 4) && (Minor >= 0) && (Build >= 30319) && (Revision >= 17929))
                return @".NET 4.5 RTM or later";
            //4.0.30319.17626 = .NET 4.5 RC
            if ((Major >= 4) && (Minor >= 0) && (Build >= 30319) && (Revision >= 17626))
                return @".NET 4.5 RC or later";
            //4.0.30319.17020.NET 4.5 Preview, September 2011
            if ((Major >= 4) && (Minor >= 0) && (Build >= 30319) && (Revision >= 17020))
                return @".NET 4.5 Preview, September 2011 or later";
            //4.0.30319.2034 = .NET 4.0 on Windows XP SP3, 7, 7 SP1(with MS14 - 009 LDR security update)
            if ((Major >= 4) && (Minor >= 0) && (Build >= 30319) && (Revision >= 2034))
                return @".NET 4.0 on Windows XP SP3, 7, 7 SP1(with MS14 - 009 LDR security update) or later";
            //4.0.30319.1026 = .NET 4.0 on Windows XP SP3, 7, 7 SP1(with MS14 - 057 GDR security update)
            if ((Major >= 4) && (Minor >= 0) && (Build >= 30319) && (Revision >= 1026))
                return @".NET 4.0 on Windows XP SP3, 7, 7 SP1(with MS14 - 057 GDR security update) or later";
            //4.0.30319.1022 = .NET 4.0 on Windows XP SP3, 7, 7 SP1(with MS14 - 009 GDR security update)
            if ((Major >= 4) && (Minor >= 0) && (Build >= 30319) && (Revision >= 1022))
                return @".NET 4.0 on Windows XP SP3, 7, 7 SP1(with MS14 - 009 GDR security update) or later";
            //4.0.30319.1008 = .NET 4.0 on Windows XP SP3, 7, 7 SP1(with MS13 - 052 GDR security update)
            if ((Major >= 4) && (Minor >= 0) && (Build >= 30319) && (Revision >= 1008))
                return @".NET 4.0 on Windows XP SP3, 7, 7 SP1(with MS13 - 052 GDR security update) or later";
            //4.0.30319.544 = .NET 4.0 on Windows XP SP3, 7, 7 SP1(with MS12 - 035 LDR security update)
            if ((Major >= 4) && (Minor >= 0) && (Build >= 30319) && (Revision >= 544))
                return @".NET 4.0 on Windows XP SP3, 7, 7 SP1(with MS12 - 035 LDR security update) or later";
            //4.0.30319.447   yes built by: RTMLDR, .NET 4.0 Platform Update 1, April 2011
            if ((Major >= 4) && (Minor >= 0) && (Build >= 30319) && (Revision >= 447))
                return @"built by: RTMLDR, .NET 4.0 Platform Update 1, April 2011 or later";
            //4.0.30319.431   yes built by: RTMLDR, .NET 4.0 GDR Update, March 2011 / with VS 2010 SP1 / or.NET 4.0 Update
            if ((Major >= 4) && (Minor >= 0) && (Build >= 30319) && (Revision >= 431))
                return @"built by: RTMLDR, .NET 4.0 GDR Update, March 2011 / with VS 2010 SP1 / or.NET 4.0 Update or later";
            //4.0.30319.296 = .NET 4.0 on Windows XP SP3, 7(with MS12 - 074 GDR security update)
            if ((Major >= 4) && (Minor >= 0) && (Build >= 30319) && (Revision >= 296))
                return @".NET 4.0 on Windows XP SP3, 7(with MS12 - 074 GDR security update) or later";
            //4.0.30319.276 = .NET 4.0 on Windows XP SP3 (4.0.3 Runtime update)
            if ((Major >= 4) && (Minor >= 0) && (Build >= 30319) && (Revision >= 276))
                return @".NET 4.0 on Windows XP SP3 (4.0.3 Runtime update) or later";
            //4.0.30319.269 = .NET 4.0 on Windows XP SP3, 7, 7 SP1(with MS12 - 035 GDR security update)
            if ((Major >= 4) && (Minor >= 0) && (Build >= 30319) && (Revision >= 269))
                return @".NET 4.0 on Windows XP SP3, 7, 7 SP1(with MS12 - 035 GDR security update) or later";
            //4.0.30319.1 yes built by: RTMRel, .NET 4.0 RTM Release, April 2010
            if ((Major >= 4) && (Minor >= 0) && (Build >= 30319) && (Revision >= 1))
                return @"built by: RTMRel, .NET 4.0 RTM Release, April 2010 or later";

            //4.0.30128.1     built by: RC1Rel, .NET 4.0 Release Candidate, Feb 2010
            if ((Major >=4) && (Minor >=0) && (Build >= 30128) && (Revision >= 1))
                return @"built by: RC1Rel, .NET 4.0 Release Candidate, Feb 2010 or later";
            //4.0.21006.1     built by: B2Rel, .NET 4.0 Beta2, Oct 2009
            if ((Major >=4) && (Minor >=0) && (Build >= 21006) && (Revision >=1))
                return @"built by: B2Rel, .NET 4.0 Beta2, Oct 2009 or later";
            //4.0.20506.1     built by: Beta1, .NET 4.0 Beta1, May 2009
            if ((Major >=4) && (Minor >=0) && (Build >= 20506) && (Revision >=1))
                return @"built by: Beta1, .NET 4.0 Beta1, May 2009 or later";
            //4.0.11001.1     built by: CTP2 VPC, .NET 4.0 CTP, October 2008
            if ((Major >=4) && (Minor >=0) && (Build >= 11001) && (Revision >=1))
                return @"built by: CTP2 VPC, .NET 4.0 CTP, October 2008 or later";

            //3.5.30729.5420  yes built by: Win7SP1, .NET 3.5.1 Sicherheits - Update, 12 April 2011
            if ((Major >=3) && (Minor >=5) && (Build >= 30729) && (Revision >= 5420))
                return @"built by: Win7SP1, .NET 3.5.1 Sicherheits - Update, 12 April 2011 or later";
            //3.5.30729.5004  yes built by: NetFXw7 / Windows 7..Rel., Jan 2010 / +Data functions KB976127 .NET 3.5 SP1
            if ((Major >=3) && (Minor >=5) && (Build >= 30729) && (Revision >= 5004))
                return @"built by: NetFXw7 / Windows 7..Rel., Jan 2010 / +Data functions KB976127 .NET 3.5 SP1 or later";
            //3.5.30729.4466  yes built by: NetFXw7 / Windows XP..Rel. , Jan 2010 / +Data functions KB976127 .NET 3.5 SP1
            if ((Major >=3) && (Minor >=5) && (Build >= 30729) && (Revision >= 4466))
                return @"built by: NetFXw7 / Windows XP..Rel. , Jan 2010 / +Data functions KB976127 .NET 3.5 SP1 or later";
            //3.5.30729.4926  yes built by: NetFXw7 / Windows 7 Release, Oct 2009 / .NET 3.5 SP1 + Hotfixes
            if ((Major >=3) && (Minor >=5) && (Build >= 30729) && (Revision >= 4926))
                return @"built by: NetFXw7 / Windows 7 Release, Oct 2009 / .NET 3.5 SP1 + Hotfixes or later";
            //3.5.30729.4918      built by: NetFXw7 / Windows 7 Release Candidate, June 2009
            if ((Major >=3) && (Minor >=5) && (Build >= 30729) && (Revision >= 4918))
                return @"built by: NetFXw7 / Windows 7 Release Candidate, June 2009 or later";
            //3.5.30729.196   yes built by: QFE, .NET 3.5 Family Update Vista / W2008, Dec 2008
            if ((Major >= 3) && (Minor >= 5) && (Build >= 30729) && (Revision >=196))
                return @"built by: QFE, .NET 3.5 Family Update Vista / W2008, Dec 2008 or later";
            //3.5.30729.1 yes built by: SP, .NET 3.5 SP1, Aug 2008
            if ((Major >= 3) && (Minor >= 5) && (Build >= 30729) && (Revision >=1))
                return @"built by: SP, .NET 3.5 SP1, Aug 2008 or later";

            //3.5.30428.1         built by: SP1Beta1, .NET 3.5 SP1 BETA1, May 2008
            if ((Major >=3) && (Minor >=5) && (Build >= 30428) && (Revision >=1))
                return @"built by: SP1Beta1, .NET 3.5 SP1 BETA1, May 2008 or later";
            //3.5.21022.8 yes built by: RTM, Jan 2008
            if ((Major >=3) && (Minor >=5) && (Build >= 21022) && (Revision >= 8))
                return @"built by: RTM, Jan 2008 or later";
            //3.5.20706.1     built by: Beta2, Orcas Beta2, Oct 2007
            if ((Major >=3) && (Minor >=5) && (Build >= 20706) && (Revision >= 1))
                return @"built by: Beta2, Orcas Beta2, Oct 2007 or later";
            //3.5.20526.0     built by: MCritCTP, Orcas Beta1, Mar 2007
            if ((Major >=3) && (Minor >=5) && (Build >= 20526) && (Revision >=0))
                return @"built by: MCritCTP, Orcas Beta1, Mar 2007 or later";

            //3.0.6920.1500   yes built by: QFE, Family Update Vista / W2008, Dez 2008, KB958483
            if ((Major >=3) && (Minor >=0) && (Build >= 6920) && (Revision >= 1500))
                return @"built by: QFE, Family Update Vista / W2008, Dez 2008, KB958483 or later";
            //3.0.4506.4926   yes(NetFXw7.030729 - 4900) / Windows 7 Release, Oct 2009
            if ((Major >=3) && (Minor >=0) && (Build >= 4506) && (Revision >= 4926))
                return @"(NetFXw7.030729 - 4900) / Windows 7 Release, Oct 2009 or later";
            //3.0.4506.4918(NetFXw7.030729 - 4900) / Windows 7 Release Candidate, June 2009
            if ((Major >=3) && (Minor >=5) && (Build >= 4506) && (Revision >= 4918))
                return @"(NetFXw7.030729 - 4900) / Windows 7 Release Candidate, June 2009 or later";
            //3.0.4506.2152       3.0.4506.2152(SP.030729 - 0100) / .NET 4.0 Beta1 / May 2009
            if ((Major >= 3) && (Minor >= 5) && (Build >= 4506) && (Revision >= 2152))
                return @"3.0.4506.2152(SP.030729 - 0100) / .NET 4.0 Beta1 / May 2009 or later";
            //3.0.4506.2123   yes(NetFX.030618 - 0000).NET 3.0 SP2, Aug 2008
            if ((Major >= 3) && (Minor >= 5) && (Build >= 4506) && (Revision >= 2123))
                return @"s(NetFX.030618 - 0000).NET 3.0 SP2, Aug 2008 or later";
            //3.0.4506.2062(SP1Beta1.030428 - 0100), .NET 3.0 SP1 BETA1, May 2008
            if ((Major >= 3) && (Minor >= 5) && (Build >= 4506) && (Revision >= 2062))
                return @"(SP1Beta1.030428 - 0100), .NET 3.0 SP1 BETA1, May 2008 or later";
            //3.0.4506.590(winfxredb2.004506 - 0590), Orcas Beta2, Oct 2007
            if ((Major >= 3) && (Minor >= 5) && (Build >= 4506) && (Revision >= 590))
                return @"(winfxredb2.004506 - 0590), Orcas Beta2, Oct 2007 or later";
            //3.0.4506.577(winfxred.004506 - 0577), Orcas Beta1, Mar 2007
            if ((Major >= 3) && (Minor >= 5) && (Build >= 4506) && (Revision >= 577))
                return @"(winfxred.004506 - 0577), Orcas Beta1, Mar 2007 or later";
            //3.0.4506.30 yes Release (.NET Framework 3.0) Nov 2006
            if ((Major >= 3) && (Minor >= 5) && (Build >= 4506) && (Revision >= 30))
                return @"Release (.NET Framework 3.0) Nov 2006 or later";
            //3.0.4506.25 yes(WAPRTM.004506 - 0026) Vista Ultimate, Jan 2007
            if ((Major >= 3) && (Minor >= 5) && (Build >= 4506) && (Revision >= 25))
                return @"(WAPRTM.004506 - 0026) Vista Ultimate, Jan 2007 or later";

            //2.0.50727.4927  yes(NetFXspW7.050727 - 4900) / Windows 7 Release, Oct 2009
            if ((Major >=2) && (Minor >=0) && (Build >= 50727) && (Revision >= 4927))
                return @"(NetFXspW7.050727 - 4900) / Windows 7 Release, Oct 2009 or later";
            //2.0.50727.4918(NetFXspW7.050727 - 4900) / Windows 7 Release Candidate, June 2009
            if ((Major >= 2) && (Minor >= 0) && (Build >= 50727) && (Revision >= 4918))
                return @"(NetFXspW7.050727 - 4900) / Windows 7 Release Candidate, June 2009 or later";
            //2.0.50727.4200  yes(NetFxQFE.050727 - 4200).NET 2.0 SP2, KB974470, Securityupdate, Oct 2009
            if ((Major >= 2) && (Minor >= 0) && (Build >= 50727) && (Revision >= 4200))
                return @"(NetFxQFE.050727 - 4200).NET 2.0 SP2, KB974470, Securityupdate, Oct 2009 or later";
            //2.0.50727.3603(GDR.050727 - 3600).NET 4.0 Beta 2, Oct 2009
            if ((Major >= 2) && (Minor >= 0) && (Build >= 50727) && (Revision >= 3603))
                return @"(GDR.050727 - 3600).NET 4.0 Beta 2, Oct 2009 or later";
            //2.0.50727.3082  yes(QFE.050727 - 3000), .NET 3.5 Family Update XP / W2003, Dez 2008, KB958481
            if ((Major >= 2) && (Minor >= 0) && (Build >= 50727) && (Revision >= 3082))
                return @"(QFE.050727 - 3000), .NET 3.5 Family Update XP / W2003, Dez 2008, KB958481 or later";
            //2.0.50727.3074  yes(QFE.050727 - 3000), .NET 3.5 Family Update Vista / W2008, Dez 2008, KB958481
            if ((Major >= 2) && (Minor >= 0) && (Build >= 50727) && (Revision >= 3074))
                return @"(QFE.050727 - 3000), .NET 3.5 Family Update Vista / W2008, Dez 2008, KB958481 or later";
            //2.0.50727.3053  yes(netfxsp.050727 - 3000), .NET 2.0 SP2, Aug 2008
            if ((Major >= 2) && (Minor >= 0) && (Build >= 50727) && (Revision >= 3053))
                return @"yes(netfxsp.050727 - 3000), .NET 2.0 SP2, Aug 2008 or later";
            //2.0.50727.3031(netfxsp.050727 - 3000), .NET 2.0 SP2 Beta 1, May 2008
            if ((Major >= 2) && (Minor >= 0) && (Build >= 50727) && (Revision >= 3031))
                return @"(netfxsp.050727 - 3000), .NET 2.0 SP2 Beta 1, May 2008 or later";
            //2.0.50727.1434  yes(REDBITS.050727 - 1400), Windows Server 2008 and Windows Vista SP1, Dez 2007
            if ((Major >= 2) && (Minor >= 0) && (Build >= 50727) && (Revision >= 1434))
                return @"(REDBITS.050727 - 1400), Windows Server 2008 and Windows Vista SP1, Dez 2007 or later";
            //2.0.50727.1433  yes(REDBITS.050727 - 1400), .NET 2.0 SP1 Release, Nov 2007, http://www.microsoft.com/downloads/details.aspx?FamilyID=79bc3b77-e02c-4ad3-aacf-a7633f706ba5
            if ((Major >= 2) && (Minor >= 0) && (Build >= 50727) && (Revision >= 1433))
                return @"(REDBITS.050727 - 1400), .NET 2.0 SP1 Release, Nov 2007 or later";
            //2.0.50727.1378(REDBITSB2.050727 - 1300), Orcas Beta2, Oct 2007
            if ((Major >= 2) && (Minor >= 0) && (Build >= 50727) && (Revision >= 1378))
                return @"(REDBITSB2.050727 - 1300), Orcas Beta2, Oct 2007 or later";
            //2.0.50727.1366(REDBITS.050727 - 1300), Orcas Beta1, Mar 2007
            if ((Major >= 2) && (Minor >= 0) && (Build >= 50727) && (Revision >= 1366))
                return @"(REDBITS.050727 - 1300), Orcas Beta1, Mar 2007 or later";
            //2.0.50727.867   yes(VS Express Edition 2005 SP1), Apr 2007, http://www.microsoft.com/downloads/details.aspx?FamilyId=7B0B0339-613A-46E6-AB4D-080D4D4A8C4E
            if ((Major >= 2) && (Minor >= 0) && (Build >= 50727) && (Revision >= 867))
                return @"(VS Express Edition 2005 SP1), Apr 2007 or later";
            //2.0.50727.832(Fix x86 VC++2005), Apr 2007, http://support.microsoft.com/kb/934586/en-us
            if ((Major >= 2) && (Minor >= 0) && (Build >= 50727) && (Revision >= 832))
                return @"(Fix x86 VC++2005), Apr 2007 or later";
            //2.0.50727.762   yes(VS TeamSuite SP1), http://www.microsoft.com/downloads/details.aspx?FamilyId=BB4A75AB-E2D4-4C96-B39D-37BAF6B5B1DC
            if ((Major >= 2) && (Minor >= 0) && (Build >= 50727) && (Revision >= 762))
                return @"(VS TeamSuite SP1) or later";
            //2.0.50727.312   yes(rtmLHS.050727 - 3100) Vista Ultimate, Jan 2007
            if ((Major >= 2) && (Minor >= 0) && (Build >= 50727) && (Revision >= 312))
                return @"(rtmLHS.050727 - 3100) Vista Ultimate, Jan 2007 or later";
            //2.0.50727.42    yes Release (.NET Framework 2.0) Oct 2005
            if ((Major >= 2) && (Minor >= 0) && (Build >= 50727) && (Revision >= 42))
                return @"Release (.NET Framework 2.0) Oct 2005 or later";
            //2.0.50727.26        Version 2.0(Visual Studio Team System 2005 Release Candidate) Oct 2005
            if ((Major >= 2) && (Minor >= 0) && (Build >= 50727) && (Revision >= 26))
                return @"Version 2.0(Visual Studio Team System 2005 Release Candidate) Oct 2005 or later";

            //2.0.50712       Version 2.0(Visual Studio Team System 2005(Drop3) CTP) July 2005
            if ((Major >=2) && (Minor >=0) && (Build >= 50712))
                return @"Version 2.0(Visual Studio Team System 2005(Drop3) CTP) July 2005 or later";
            //2.0.50215       Version 2.0(WinFX SDK for Indigo / Avalon 2005 CTP) July 2005
            if ((Major >=2) && (Minor >=0) && (Build >= 50215))
                return @"Version 2.0(WinFX SDK for Indigo / Avalon 2005 CTP) July 2005 or later";
            //2.0.50601.0     Version 2.0(Visual Studio.NET 2005 CTP) June 2005
            if ((Major >=2) && (Minor >=0) && (Build >= 50601) && (Revision >=0))
                return @"Version 2.0(Visual Studio.NET 2005 CTP) June 2005 or later";
            //2.0.50215.44        Version 2.0(Visual Studio.NET 2005 Beta 2, Visual Studio Express Beta 2) Apr 2005
            if ((Major >=2) && (Minor >=0) && (Build >= 50215) && (Revision >= 44))
                return @"Version 2.0(Visual Studio.NET 2005 Beta 2, Visual Studio Express Beta 2) Apr 2005 or later";
            //2.0.50110.28        Version 2.0(Visual Studio.NET 2005 CTP, Professional Edition) Feb 2005
            if ((Major >=2) && (Minor >=0) && (Build >= 50110) && (Revision >=28))
                return @"Version 2.0(Visual Studio.NET 2005 CTP, Professional Edition) Feb 2005 or later";
            //2.0.41115.19        Version 2.0(Visual Studio.NET 2005 Beta 1, Team System Refresh) Dec 2004
            if ((Major >=2 ) && (Minor >=0 ) && (Build >= 41115) && (Revision >= 19))
                return @"Version 2.0(Visual Studio.NET 2005 Beta 1, Team System Refresh) Dec 2004 or later";
            //2.0.40903.0         Version 2.0(Whidbey CTP, Visual Studio Express) Oct 2004
            if ((Major >=2) && (Minor >=0) && (Build >= 40903) && (Revision >=0))
                return @"Version 2.0(Whidbey CTP, Visual Studio Express) Oct 2004 or later";
            //2.0.40607.85        Version 2.0(Visual Studio.NET 2005 Beta 1, Team System Refresh) Aug 2004 *
            if ((Major >=2) && (Minor >=0) && (Build >= 40607) && (Revision >= 85))
                return @"Version 2.0(Visual Studio.NET 2005 Beta 1, Team System Refresh) Aug 2004 * or later";
            //2.0.40607.42        Version 2.0(SQL Server Yukon Beta 2) July 2004
            if ((Major >=2) && (Minor >=0) && (Build >= 40607) && (Revision >= 42))
                return @"Version 2.0(SQL Server Yukon Beta 2) July 2004 or later";
            //2.0.40607.16        Version 2.0(Visual Studio.NET 2005 Beta 1, TechEd Europe 2004) June 2004
            if ((Major >=2) && (Minor >=0) && (Build >= 40607) && (Revision >= 16))
                return @"Version 2.0(Visual Studio.NET 2005 Beta 1, TechEd Europe 2004) June 2004 or later";
            //2.0.40301.9         Version 2.0(Whidbey CTP, WinHEC 2004) March 2004 *
            if ((Major >=0) && (Minor >=0) && (Build >= 40301) && (Revision >=9))
                return @"Version 2.0(Whidbey CTP, WinHEC 2004) March 2004 * or later";

            //1.2.30703.27        Version 1.2(Whidbey Alpha, PDC 2004) Nov 2003 *
            if ((Major >=1) && (Minor >=2) && (Build >= 30703) && (Revision >= 27))
                return @"Version 1.2(Whidbey Alpha, PDC 2004) Nov 2003 * or later";
            //1.2.21213.1     Version 1.2(Whidbey pre - Alpha build) *
            if ((Major >=1) && (Minor >=2) && (Build >= 21213) && (Revision >=1))
                return @"Version 1.2(Whidbey pre - Alpha build) * or later";

            //1.1.4322.2443   yes Version 1.1 Servicepack 1, KB953297, Oct 2009
            if ((Major >=1) && (Minor >=1) && (Build >= 4322) && (Revision >=2443))
                return @"Version 1.1 Servicepack 1, KB953297, Oct 2009 or later";
            //1.1.4322.2407   yes Version 1.1 RTM
            if ((Major >=1) && (Minor >=1) && (Build >= 4322) && (Revision >= 2407))
                return @"Version 1.1 RTM or later";
            //1.1.4322.2407       Version 1.1 Orcas Beta2, Oct 2007
            if ((Major >=1) && (Minor >=1) && (Build >= 4322) && (Revision >= 2407))
                return @"Version 1.1 Orcas Beta2, Oct 2007 or later";
            //1.1.4322.2379       Version 1.1 Orcas Beta1, Mar 2007
            if ((Major >=1) && (Minor >=1) && (Build >= 4322) && (Revision >= 2379))
                return @"Version 1.1 Orcas Beta1, Mar 2007 or later";
            //1.1.4322.2032   yes Version 1.1 SP1 Aug 2004
            if ((Major >=1) && (Minor >=1) && (Build >= 4322) && (Revision >= 2032))
                return @"Version 1.1 SP1 Aug 2004 or later";
            //1.1.4322.573    yes Version 1.1 RTM(Visual Studio.NET 2003 / Windows Server 2003) Feb 2003 *
            if ((Major >=1) && (Minor >=1) && (Build >= 4322) && (Revision >= 573))
                return @"Version 1.1 RTM(Visual Studio.NET 2003 / Windows Server 2003) Feb 2003 * or later";
            //1.1.4322.510        Version 1.1 Final Beta Oct 2002 *
            if ((Major >=1) && (Minor >=1) && (Build >= 4322) && (Revision >= 510))
                return @"Version 1.1 Final Beta Oct 2002 * or later";

            //1.0.3705.6018   yes Version 1.0 SP3 Aug 2004
            if ((Major >=1) && (Minor >=0) && (Build >= 3705) && (Revision >= 6018))
                return @"Version 1.0 SP3 Aug 2004 or later";
            //1.0.3705.288    yes Version 1.0 SP2 Aug 2002 *
            if ((Major >=1) && (Minor >=0) && (Build >= 3705) && (Revision >= 288))
                return @"Version 1.0 SP2 Aug 2002 * or later";
            //1.0.3705.209    yes Version 1.0 SP1 Mar 2002 *
            if ((Major >=1) && (Minor >=0) && (Build >= 3705) && (Revision >=209))
                return @"Version 1.0 SP1 Mar 2002 * or later";
            //1.0.3705.0  yes Version 1.0 RTM(Visual Studio.NET 2002) Feb 2002 *
            if ((Major >=1) && (Minor >=0) && (Build >= 3705) && (Revision >=0))
                return @"Version 1.0 RTM(Visual Studio.NET 2002) Feb 2002 * or later";
            //1.0.3512.0      Version 1.0 Pre - release RC3(Visual Studio.NET 2002 RC3)
            if ((Major >=1) && (Minor >=0) && (Build >= 3512) && (Revision >=0))
                return @"Version 1.0 Pre - release RC3(Visual Studio.NET 2002 RC3) or later";
            //1.0.2914.16     Version 1.0 Public Beta 2 Jun 2001 *
            if ((Major >=1) && (Minor >=0) && (Build >= 2914) && (Revision >= 16))
                return @"Version 1.0 Public Beta 2 Jun 2001 * or later";
            //1.0.2204.21         Version 1.0 Public Beta 1 Nov 2000 *
            if ((Major >=1) && (Minor >=0) && (Build >= 2204) && (Revision >=21))
                return @"Version 1.0 Public Beta 1 Nov 2000 * or later";

            return @"Unknown .NET version";
        }
    }
}

Not sure why nobody suggested following the official advice from Microsoft right here.

This is the code they recommend. Sure it's ugly, but it works.

For .NET 1-4

private static void GetVersionFromRegistry()
{
     // Opens the registry key for the .NET Framework entry. 
        using (RegistryKey ndpKey = 
            RegistryKey.OpenRemoteBaseKey(RegistryHive.LocalMachine, "").
            OpenSubKey(@"SOFTWARE\Microsoft\NET Framework Setup\NDP\"))
        {
            // As an alternative, if you know the computers you will query are running .NET Framework 4.5  
            // or later, you can use: 
            // using (RegistryKey ndpKey = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine,  
            // RegistryView.Registry32).OpenSubKey(@"SOFTWARE\Microsoft\NET Framework Setup\NDP\"))
        foreach (string versionKeyName in ndpKey.GetSubKeyNames())
        {
            if (versionKeyName.StartsWith("v"))
            {

                RegistryKey versionKey = ndpKey.OpenSubKey(versionKeyName);
                string name = (string)versionKey.GetValue("Version", "");
                string sp = versionKey.GetValue("SP", "").ToString();
                string install = versionKey.GetValue("Install", "").ToString();
                if (install == "") //no install info, must be later.
                    Console.WriteLine(versionKeyName + "  " + name);
                else
                {
                    if (sp != "" && install == "1")
                    {
                        Console.WriteLine(versionKeyName + "  " + name + "  SP" + sp);
                    }

                }
                if (name != "")
                {
                    continue;
                }
                foreach (string subKeyName in versionKey.GetSubKeyNames())
                {
                    RegistryKey subKey = versionKey.OpenSubKey(subKeyName);
                    name = (string)subKey.GetValue("Version", "");
                    if (name != "")
                        sp = subKey.GetValue("SP", "").ToString();
                    install = subKey.GetValue("Install", "").ToString();
                    if (install == "") //no install info, must be later.
                        Console.WriteLine(versionKeyName + "  " + name);
                    else
                    {
                        if (sp != "" && install == "1")
                        {
                            Console.WriteLine("  " + subKeyName + "  " + name + "  SP" + sp);
                        }
                        else if (install == "1")
                        {
                            Console.WriteLine("  " + subKeyName + "  " + name);
                        }

                    }

                }

            }
        }
    }

}

For .NET 4.5 and later

// Checking the version using >= will enable forward compatibility, 
// however you should always compile your code on newer versions of
// the framework to ensure your app works the same.
private static string CheckFor45DotVersion(int releaseKey)
{
   if (releaseKey >= 393295) {
      return "4.6 or later";
   }
   if ((releaseKey >= 379893)) {
        return "4.5.2 or later";
    }
    if ((releaseKey >= 378675)) {
        return "4.5.1 or later";
    }
    if ((releaseKey >= 378389)) {
        return "4.5 or later";
    }
    // This line should never execute. A non-null release key should mean
    // that 4.5 or later is installed.
    return "No 4.5 or later version detected";
}

private static void Get45or451FromRegistry()
{
    using (RegistryKey ndpKey = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry32).OpenSubKey("SOFTWARE\\Microsoft\\NET Framework Setup\\NDP\\v4\\Full\\")) {
        if (ndpKey != null && ndpKey.GetValue("Release") != null) {
            Console.WriteLine("Version: " + CheckFor45DotVersion((int) ndpKey.GetValue("Release")));
        }
      else {
         Console.WriteLine("Version 4.5 or later is not detected.");
      } 
    }
}

        public static class DotNetHelper
{
    public static Version InstalledVersion
    {
        get
        {
            string framework = null;

            try
            {
                using (var ndpKey =
            Registry.LocalMachine.OpenSubKey("SOFTWARE\\Microsoft\\NET Framework Setup\\NDP\\v4\\Full\\"))
                {
                    if (ndpKey != null)
                    {
                        var releaseKey = ndpKey.GetValue("Release");
                        if (releaseKey != null)
                        {
                            framework = CheckFor45PlusVersion(Convert.ToInt32(releaseKey));
                        }
                        else
                        {
                            string[] versionNames = null;
                            using (var installedVersions =
                                Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\NET Framework Setup\NDP"))
                            {
                                if (installedVersions != null) versionNames = installedVersions.GetSubKeyNames();
                            }


                            try
                            {
                                if (versionNames != null && versionNames.Length > 0)
                                {
                                    framework = versionNames[versionNames.Length - 1].Remove(0, 1);
                                }
                            }
                            catch (FormatException)
                            {

                            }
                        }
                    }
                }
            }
            catch (SecurityException)
            {
            }

            return framework != null ? new Version(framework) : null;
        }
    }

    private static string CheckFor45PlusVersion(int releaseKey)
    {
        if (releaseKey >= 460798)
            return "4.7";
        if (releaseKey >= 394802)
            return "4.6.2";
        if (releaseKey >= 394254)
            return "4.6.1";
        if (releaseKey >= 393295)
            return "4.6";
        if (releaseKey >= 379893)
            return "4.5.2";
        if (releaseKey >= 378675)
            return "4.5.1";
        // This code should never execute. A non-null release key should mean
        // that 4.5 or later is installed.
        return releaseKey >= 378389 ? "4.5" : null;
    }
}

This class allows your application to throw out a graceful notification message rather than crash and burn if it couldn't find the proper .NET version. All you need to do is this in your main code:

[STAThread]
static void Main(string[] args)
{
    if (!DotNetUtils.IsCompatible())
        return;
   . . .
}

By default it takes 4.5.2, but you can tweak it to your liking, the class (feel free to replace MessageBox with Console):

Updated for 4.8:

public class DotNetUtils
{
    public enum DotNetRelease
    {
        NOTFOUND,
        NET45,
        NET451,
        NET452,
        NET46,
        NET461,
        NET462,
        NET47,
        NET471,
        NET472,
        NET48,
    }

    public static bool IsCompatible(DotNetRelease req = DotNetRelease.NET452)
    {
        DotNetRelease r = GetRelease();
        if (r < req)
        {
            MessageBox.Show(String.Format("This this application requires {0} or greater.", req.ToString()));
            return false;
        }
        return true;
    }

    public static DotNetRelease GetRelease(int release = default(int))
    {
        int r = release != default(int) ? release : GetVersion();
        if (r >= 528040) return DotNetRelease.NET48;
        if (r >= 461808) return DotNetRelease.NET472;
        if (r >= 461308) return DotNetRelease.NET471;
        if (r >= 460798) return DotNetRelease.NET47;
        if (r >= 394802) return DotNetRelease.NET462;
        if (r >= 394254) return DotNetRelease.NET461;
        if (r >= 393295) return DotNetRelease.NET46;
        if (r >= 379893) return DotNetRelease.NET452;
        if (r >= 378675) return DotNetRelease.NET451;
        if (r >= 378389) return DotNetRelease.NET45;
        return DotNetRelease.NOTFOUND;
    }

    public static int GetVersion()
    {
        int release = 0;
        using (RegistryKey key = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry32)
                                            .OpenSubKey("SOFTWARE\\Microsoft\\NET Framework Setup\\NDP\\v4\\Full\\"))
        {
            release = Convert.ToInt32(key.GetValue("Release"));
        }
        return release;
    }
}

Easily extendable when they add a new version later on. I didn't bother with anything before 4.5 but you get the idea.


I tried to combine all the answers into a single whole.

Using:

NetFrameworkUtilities.GetVersion() will return the currently available Version of the .NET Framework at this time or null if it is not present.

This example works in .NET Framework versions 3.5+. It does not require administrator rights.

I want to note that you can check the version using the operators < and > like this:

var version = NetFrameworkUtilities.GetVersion();
if (version != null && version < new Version(4, 5))
{
    MessageBox.Show("Your .NET Framework version is less than 4.5");
}

Code:

using System;
using System.Linq;
using Microsoft.Win32;

namespace Utilities
{
    public static class NetFrameworkUtilities
    {
        public static Version GetVersion() => GetVersionHigher4() ?? GetVersionLowerOr4();

        private static Version GetVersionLowerOr4()
        {
            using (var key = Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\NET Framework Setup\NDP"))
            {
                var names = key?.GetSubKeyNames();

                //version names start with 'v', eg, 'v3.5' which needs to be trimmed off before conversion
                var text = names?.LastOrDefault()?.Remove(0, 1);
                if (string.IsNullOrEmpty(text))
                {
                    return null;
                }

                return text.Contains('.')
                    ? new Version(text)
                    : new Version(Convert.ToInt32(text), 0);
            }
        }

        private static Version GetVersionHigher4()
        {
            using (var key = Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full"))
            {
                var value = key?.GetValue("Release");
                if (value == null)
                {
                    return null;
                }

                // Checking the version using >= will enable forward compatibility,  
                // however you should always compile your code on newer versions of 
                // the framework to ensure your app works the same. 
                var releaseKey = Convert.ToInt32(value);
                if (releaseKey >= 461308) return new Version(4, 7, 1);
                if (releaseKey >= 460798) return new Version(4, 7);
                if (releaseKey >= 394747) return new Version(4, 6, 2);
                if (releaseKey >= 394254) return new Version(4, 6, 1);
                if (releaseKey >= 381029) return new Version(4, 6);
                if (releaseKey >= 379893) return new Version(4, 5, 2);
                if (releaseKey >= 378675) return new Version(4, 5, 1);
                if (releaseKey >= 378389) return new Version(4, 5);

                // This line should never execute. A non-null release key should mean 
                // that 4.5 or later is installed. 
                return new Version(4, 5);
            }
        }
    }
}

Try this one:

string GetFrameWorkVersion()
    {
        return System.Runtime.InteropServices.RuntimeEnvironment.GetSystemVersion();
    }

This is the solution I landed on:

private static string GetDotNetVersion()
{
  var v4 = (string)Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full", false)?.GetValue("Version");
  if(v4 != null)
    return v4;
  var v35 = (string)Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\NET Framework Setup\NDP\v3.5", false)?.GetValue("Version");
  if(v35 != null)
    return v35;
  var v3 = (string)Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\NET Framework Setup\NDP\v3.0", false)?.GetValue("Version");
  return v3 ?? "< 3";
}

I had a situation where my .NET 4.0 class library might be called from an .NET 4.0 or higher version assemblies.

A specific method call would only work if executed from an 4.5+ assembly.

In Order to decide if I should call the method or not I needed to determine the current executing framework version and this is a pretty good solution for that

var frameworkName = new System.Runtime.Versioning.FrameworkName(
    AppDomain.CurrentDomain.SetupInformation.TargetFrameworkName
);

if (frameworkName.Version >= new Version(4, 5)) 
{
    // run code
}