This book focuses on a number of approaches of assessment associated with information systems (IS) effectiveness. Fundamental guidelines for research in this area have been derived, and a novel model of IS effectiveness has been proposed. A process based assessment method (PB-ISAM) based on the proposed effectiveness model has been elaborated. The new model and the new assessment method have been evaluated via three case studies in three different contexts. Specific implications have been drawn concerning the relationships between processes and the information system assessed. The three case studies have provided insight into the IS effectiveness field and for future work. This book will provide researchers and professionals with a comprehensive reference for effective use of information systems in organizations throughout the world - only by evaluating the effectiveness of information systems, we can justify their use and continue to develop their quality.