This book provides an insight into established techniques which help developers to overcome the complexity of software development by constructing models of software systems in early design stages. The analysis and testing of models allows feedback before an expensive commitment is made to detailed design and coding. Aimed at software developers in industry and university students in software engineering courses, the text provides a remarkable new introduction to modelling using a leading ISO Standard VDM-SL. The text breaks new ground by combining training in modelling techniques with commercial-strength tool support on a PC Windows platform.