Microsoft today announced that coinciding with the final release of Visual Studio 2008 we will release much of the source code to the .NET Framework Libraries under the Microsoft Reference License. This means that anyone who accepts the license will be able to browse and view source code. The set of libraries initially includes the Base Class Libraries (System namespace, IO, Text, Collections, CodeDom, Regular Expressions, etc), ASP.NET, WinForms, and WPF . Microsoft will add to this list as time goes on.
There are two ways people will access the source code:
1) They will download a package with all the source, and then they will be able to install and browse locally
2) VS 2008 integration will enable developers to debug from their own source code into the .NET Framework source code. We’ll provide symbols for our source on an internet-accessible source-server; to enable this experience, the developer needs to set up the URI for the server. When developers are stepping through code, if they wish, they will be able to step into the source code for the .NET base class libraries.
For more information check out this podcast interview with Shawn Burke, also this post from Scott Guthrie for how it will look in VS 2008.
Source:→ MSDN Blogs