If you look up "abstract base class" at Microsoft, you will get hits on C# and C++ pages that may not help you a lot if you're looking for help in VB.NET. The problem here is that VB doesn't use the same keywords. In VB.NET, these classes are formally called "MustInherit" classes. But the concept - and the words that are usually used to describe them - originated in C. It's a tradition that we're stuck with. This new Quick Tip shows how it works.