The purpose of this book is to provide a detailed understanding of the evolutionary approach to the development of computerized information systems. It does this by describing the principles of evolutionary development and showing how they relate to the more traditional approaches to systems analysis and design. The book goes on to illustrate the approach by providing a very detailed example of an Evolutionary Development Methodology. This methodology is based on the use of well-proven tools and techniques from the standard structured systems analysis and design toolkit, built into a framework which supports the use of evolutionary prototyping. The various modelling techniques within the methodology (eg DFDs, Entity models, etc) are described in sufficient detail to enable a student or junior analyst to understand and develop skills in their use. This example methodology, which aims to be a thorough and fully comprehensive approach to evolutionary development, is offered in the book as itself a kind of "prototype", in that individual analysts and (more likely) systems development departments of organizations are invited to take it as a starting point, and "tailor" it to suit their own particular needs. The book concludes by examining in more detail some of the implications of the evolutionary approach to development. These include its relationship to project management, and the problems inherent in migration from a more traditional approach. The whole future of systems development methodologies is discussed, and the impact of modern concepts such as CASE, IPSEs, advanced application generators and knowledge-based systems considered.