Is the DbContext class defined and used differently in the version of C# for Visual Studio 2012 than in Visual Studio 2010?

I am using code written under Visual Studio 2010 as an example for a project I am writing for with Visual Studio 2012. I am having some difficulty using the DBContext class to instantiate a class. The code seems to required using the namespace System.Data.Entity.Infrastructure; and that does not seem to be defined in the newer System.Data.Entity reference.