Or like this
class Movie
{
public string FilmName { get; set; }
public string Genre { get; set; }
}
...
var listofGenres = new List<string> { "action", "comedy" };
var Movies = new List<Movie> {new Movie {Genre="action", FilmName="Film1"},
new Movie {Genre="comedy", FilmName="Film2"},
new Movie {Genre="comedy", FilmName="Film3"},
new Movie {Genre="tragedy", FilmName="Film4"}};
var movies = Movies.Join(listofGenres, x => x.Genre, y => y, (x, y) => x).ToList();