This book is a tribute to Prof. Jan in ?t Veld, who is the real founder of the Delft Systems Approach. Until a few days before he died in 2005, he was working on the English translation of his successful book Analyse van Organisatie-problemen. The eighth edition of the book appeared in the Netherlands in 2002; it represents 50 years of experience, discussion and application of a systems approach that was gradually developed and sharply defined by him. About 85,000 copies of the book had been sold by then. Unfortunately he was not able to finish the translation. The writers of this book are convinced of the value of his approach and decided to finish his work. The chapters of the Dutch book that had already been translated (by A.M.P. O?Brien) are included here with only minor changes made to them (Chapts. 2, 3, 4, 7, 8 and 9). However, we extended the theory with a conceptual view of behaviour modelling, a view that was approved by in ?t Veld himself. Besides this, in ?t Veld started his work from a purely managerial viewpoint.