Microsoft"s DCOM is a difficult but important standard. If you know some C++, the authors of Understanding DCOM can show you everything you need to know to use DCOM without a lot of jargon or needless complexity. The early sections of this book provide a remarkably clear comparison of C++ and COM. (By using what you know, you can understand what is new and different about COM, including terminology such as interfaces, instances, and GUIDs [Globally Unique Identifiers].) The authors" examples for using a simple COM object are extremely clear. They walk you through the steps required to use COM on both the client and the server side, using the Active Template Library (ATL) wizards in Visual C++ 6. After these practical examples, the authors sketch in more detail about COM with information on Microsoft IDL (MIDL), working with string data, and Object Linking and Embedding (OLE) Automation and dual interfaces. The authors do a good job of explaining the various apartment-threading models available for COM objects. They defer their discussion of the Registry until later in the book--after they present practical examples. Later sections look at callback functions and connection points, as well as the move to distributed objects and DCOM. Sections on debugging COM objects provide invaluable material on showing error messages as well as some tips on building COM objects using Visual C++ features. If you are a programmer who has been a bit baffled by DCOM, this book manages to make a difficult topic digestible. It presents a good amount of technical material but uses practical examples rather than theory to teach the reader how to be productive with DCOM. --Richard Dragan