The c# version and .Net Framework

These are the versions of C# known about at the time of this writing:
C# 1.0 released with .NET 1.0 and VS2002 (January 2002)

C# 1.2 (bizarrely enough); released with .NET 1.1 and VS2003 (April 2003). First version to call

Dispose

on

IEnumerator

s which implemented

IDisposable

. A few other small features.

C# 2.0 released with .NET 2.0 and VS2005 (November
2005). Major new features: generics, anonymous methods, nullable types,
iterator blocks

C# 3.0 released with .NET 3.5 and VS2008 (November
2007). Major new features: lambda expressions, extension methods,
expression trees, anonymous types, implicit typing (

var

), query expressions

C# 4.0 released with .NET 4 and VS2010 (April 2010). Major new features: late binding (

dynamic

), delegate and interface generic variance, more COM support, named arguments and optional parameters

C# 5.0 released with .NET 4.5 and VS2012 (August 2012). Major features: async programming, caller info attributes. Breaking change: loop variable closure.

C# 6.0 released with .NET 4.6 and VS2015 (July 2015). Implemented by Roslyn.
Features: initializers for automatically implemented properties, using
directives to import static members, exception filters, binary literals
and digit separators, indexed members and element initializers,

await

in

catch

and

finally

, extension

Add

methods in collection initializers.

There is no such thing as C# 3.5 - the cause of confusion here is
that the C# 3.0 is present in .NET 3.5. The language and framework are
versioned independently, however - as is the CLR, which is at version
2.0 for .NET 2.0 through 3.5, .NET 4 introducing CLR 4.0, service packs
notwithstanding. The CLR in .NET 4.5 has various improvements, but the
versioning is unclear: in some places it may be referred to as CLR 4.5 (this MSDN page used to refer to it that way, for example), but the

Environment.Version

property still reports 4.0.xxx.
More detailed information about the relationship between the language, runtime and framework versions is available on the C# in Depth
site. This includes information about which features of C# 3.0 you can
use when targeting .NET 2.0. (If anyone wants to bring all of the
content into this wiki answer, they're welcome to.)