Software is pervasive, error-prone, expensive to develop and, as an engineering medium, extraordinarily seductive. Some of the major challenges in software development lie not so much in the details of design but in gaining confidence that the software under development will actually meet its requirements. 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 on software engineering courses, the text provides a remarkable new introduction to modelling using a leading technology: 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. Teaching is done by example with modelling techniques being introduced through a series of studies derived from industrial applications. At each stage the main components of the modelling technology are introduced as they are needed. The tool included with the book allows readers to check their understanding by developing their own models, validating them by syntax- and type-checking, execution and testing. The authors, who are leading authorities on the use of modelling techniques in software development, have based the book on successful material from industrial and university training courses given in North America, Europe and Asia.