About GUIDs, UUIDs, and CLSIDs

COM objects are assigned a 16-byte ID number, so that the operating system can identify the application that manages the object. (By application, we mean a COM DLL or COM executable file.) This 16-byte value assigned to objects is commonly called a GUID (Globally Unique Identifier), UUID (Universally Unique Identifier), or CLSID (Class Identifier).

In the Designer COM API Reference, the GUID for each interface appears before its list of methods and properties.

Regardless of the terminology used (GUID, UUID, or CLSID), the ID number is used by the operating system to identify each object, irrespective of other names used by programmers. If two programmers inadvertently assign the same name to an interface or method, the system can determine which application to call by looking at the object's ID number.