Attendees will learn how to architect safely extensible component systems. The tutorial introduces to the concepts of component-oriented programming before presenting and explaining compound documents as an application example of extensible component systems. Creation of an add-on component to this system will be demonstrated. Finally, architecting for safe extension will be discussed. The matter will be illustrated with a small case study, exemplifying a common type of pitfall and showing a solution pattern. For the demonstrations, Component Pascal will be used. Component Pascal is designed specifically for programming extensible systems and for specifying architectural properties. The IDE used in the demo can be downloaded for free from our Web server.'