.NET and COM Interoperability Handbook, The

Using ActiveX Controls in Managed Code

ActiveX controls have always been one of the most misunderstood COM-based technologies. Microsoft didn't help the situation by changing the definition of what an ActiveX control is several times. The current definition of an ActiveX control is that it is a COM object that supports the IUnknown interface. ActiveX controls usually support many other interfaces, but all other interfaces should be viewed as optional and a container should not rely on these interfaces being supported.

However, to most people, an ActiveX control is a COM object that has a user interface and supports a special set of interfaces—IOleControl, IOleIn-PlaceObject, IDataObject, and so forth—that allow it to be hosted inside of (and ...