Prototyping, a method and technique frequently used in many engineering disciplines, has been adopted as a technique in software engineering to improve the calculation of new projects involving risks. However, there has so far been a lack of documented experience with the use of prototyping in industrial software production. The paper tries to close this gap. First, we introduce central prototyping concepts and terminology. We also present five industrial software projects in which explicit use was made of prototyping. Based on our analysis of these projects we present the resulting conclusions: prototyping means more than rapidly developing user interfaces; prototyping is a central part of a development strategy; prototyping means end user involvement; finding the right mixture of prototypes improves the development process.>