Prototyping is an approach used in evolutionary system development. In this book, the authors demonstrate which forms of prototyping can be employed to address specific problems. They examine the tools used in everyday software development to determine their suitability for prototyping and aim to clarify prototyping as a methodological concept. Part I of the book explores prototyping as a method for constructing and evaluating models, discussing traditional approaches and phase-oriented life cycle plans. Prototyping addresses fundamental issues associated with life cycle plans. The authors present their own concept of evolutionary system development. Part II discusses the extent to which technical support for evolutionary system development is feasible, reviewing various tools for supporting prototyping and indicating prospective trends. Criteria are provided to assist in the process.