How can we make sure that the software we build does what it is supposed to? 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. It uses one of the leading formal methods, VDM (Vienna Development Method), and combines training in the formalism with industry-strength tool support and examples derived from real industrial applications. The principles taught here also apply to many of the current generation of formal methods. This second edition has been updated to include advanced online tool support for formal modelling as well as up-to-date reports on real commercial applications in areas as diverse as business information systems and firmware design.