.NET - what version of the framework am I currently running in (from C#)

Question

Using C#, what is the best way to ask the .NET Runtime which version you are running under?

Answer 1

It is important to be careful about asking which version of the framework is running, and which version of the runtime is running, as they can be different. Your title and body ask subtly different questions.

@JaredPar is right on the money with the runtime version.

For framework versions, check out this closely-related post: How to detect what .NET Framework versions and service packs are installed?