In this paper, we describe the computer tool Design CPN supporting editing, simulation, and state space analysis of Coloured Petri Nets. So far, approximately 40 man-years have been invested in the development of Design CPN. It is used world-wide by more than 200 companies and research institutions. For the presentation, we draw from the experiences gained in a recent industrial application using Coloured Petri Nets in the design, validation, and veri cation of communication protocols for audio video systems.