A Theory and Practice of Program Development provides a comprehensive introduction to a software development method based on VDM-SL. Each development step is rigorously justified, and the strategies and transformations used are justified and explained ma thematically. The approach provides the formal semantics of a simple, but powerful, wide-spectrum programming language and gives a formal definition of both algorithmic and data refinement. Unlike other texts, it covers both the theory and practice of program development. Although based on VDM-SL, no knowledge of this language is assumed, thus making it widely accessible. A Theory and Practice of Program Development is intended for 3rd/4th year undergraduate and postgraduate students taking formal methods and software engineering; software developers involved in the production of provably correct computer systems and reusa ble design and the problems of reusable code.