Difference between .net framework 3-3.5-4.0

I worked on 4.0 and also the latest one 4.5 Ms.Net
There are few new concepts added to the framework.
3,3.5,4.0 and 4.5 are the frameworks of MS.Net.
Many new class libraries have been added to framework to reduce the work of programmers.
But if you want to collect more info on these frame works you can search MSDN.

Note: If you want try to load a project of Ms.net framework 4.5 in 4.0
It may load but it may not work properly due to the nice changes in the 4.5