Add Twitter Bootstrap icon to Input box

Updated Bootstrap 3.x

You can use the .input-group class like this:

<div class="input-group">
    <input type="text" class="form-control"/>
    <span class="input-group-addon">
        <i class="fa fa-search"></i>
    </span>
</div>

Working Demo in jsFiddle for 3.x

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Bootstrap 2.x

You can use the .input-append class like this:

<div class="input-append">
    <input class="span2" type="text">
    <button type="submit" class="btn">
        <i class="icon-search"></i>
    </button>
</div>

Working Demo in jsFiddle for 2.x

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Both will look like this:

If you'd like the icon inside the input box, like this:

Then see my answer to Add a Bootstrap Glyphicon to Input Box