Unlike COM, the common language runtime does not use reference counting to govern object lifetime. Instead, the garbage collector traces object references and identifies objects that can no longer be accessed by running code.
This simplifies component programming a great deal, because you do not have to worry about circular references. If a group of objects contain references to each other, but none of these object are referenced directly or indirectly from stack or shared variables, then garbage collection will automatically reclaim the memory.
http://msdn.microsoft.com/en-us/library/0t81zye4(v=vs.71).aspx
