This book deals with the development and evolution of computer-based information systems. It is an introductory text and presupposes only an elementary knowledge of programming. The purpose of the book is to explain in a simple way the main components of information systems, how they arerelated to each other, and how one develops and maintains such systems. The emphasis is on relating informal approaches to systems design with formal mathematical models of information systems. The book advocates a top-down approach to information systems design, and brings together such topics as structured systems analysis, software design, user interface design, database design, object oriented approaches, performance evaluation, CASE tools, common systems, project management, and formal systems specification models. The book covers most of the relevant aspects of information systems development. It aims to provide a basis for understanding how various approaches to information systems engineering fit together, rather than to advocate one particular development technique. Whenever new and untested techniques are mentioned, they are solidly based on well known and tested approaches such as dataflow analysis and entity-relationship modelling. Most of the book can be understood without much knowledge of mathematics.