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Each version of C# has a number of new features and generally a major theme. The major themes have been generics and nullable types in C# 2.0, LINQ in C# 3.0, and dynamic types in C# 4.0.

The major features added in each release are generally considered to be the following:

1. C#1.0/.Net1.0/vs2002
2. C#1.2/.Net1.1/vs2003
3. C# 2.0/.Net2.0/vs2005
   • Generics (framework support was added, and C# benefited from this);
   • Iterator pattern (the yield keyword);
   • Anonymous methods (the delegate keyword),
   • Nullable types, and the null coalescing operator (??). 
4. .Net3.0
5. C# 3.0/.Net3.5/vs2008
   • Anonymous types,
   • Extension methods,
   • Object initializers, collection initializers,
   • Implicitly typed local variables (var keyword),
   • Lambda expressions (=>),
   • LINQ query expression pattern. 
6. C# 4.0/.Net4.0/vs2010
   • Optional and Named Arguments
   • Dynamic typing (dynamic type)
   • Improved COM-Interop
   • Contra and Co-Variance.