The exception is the core library, mscorlib.dll, that requires no using directive to be available to our code. In this way we can use Console, Object, and many other basic stuff without explicit preprocessor using.
In this short example we use the class System::Uri that is defined in the System.dll:
System::Uri^ uri = gcnew System::Uri("http://www.heege.net");
This post is based on my reading on the book "Expert C++/CLI: .NET for Visual C++ Programmers" by Marcus Heege, APress.