Lets Say ... you are working on a COM component in C# that will wrap a Web Service. Callers of your object \ class want to use a particular web service but can not access it directly. So instead they are going to user your COM object as a proxy. One of the things your COM object must do is mirror a class in the Web Service. There is a method call to GetSomeStuff() that returns a Stuff object. public Stuff GetSomeStuff(){.... The client consuming your object has no reference to SomeWebService.NamePace.Stuff ......