PLT Scheme (DrScheme and MzScheme) supports the Component Object Model (COM) standard with two pieces of software. The first piece is MzCOM, a COM class that makes a Scheme evaluator available to COM clients. With MzCOM, programmers can embed Scheme code in programs written in mainstream languages such as C++ or Visual BASIC. Some applications can also be used as MzCOM clients. The other piece of component-support software is MysterX, which makes COM classes available to PLT Scheme programs. When needed, MysterX uses a programmable Web browser to display COM objects. We describe the technical issues encountered in building these two systems and sketch some applications. Copyright © 2002 John Wiley & Sons, Ltd.