Why is System.Web.Mvc not listed in Add References?

Question

Using C#, Visual Studio 2010.

There is a namespace called System.Web.Mvc documented on MSDN. The documentation for all the types in that namespace says that they are

Answer 1

This has changed for Visual Studio 2012 (I know the original question says VS2010, but the title will still hit on searches).

When you create a VS2012 MVC project, the system.web.mvc is placed in the packages folder which is peer to the solution. This will be referenced in the web project by default and you can find the exact path there).

If you want to reference this in a secondary project (say a supporting .dll with filters or other attributes), then you can reference it from there.