The Fourth Edition has three authors: Messrs. Kaiser, Godschalk and Chapin. The Third Edition, 1979, was written by Professors Chapin and Kaiser. The First Edition [1957] and the Second Edition [1965] were solo efforts. This history is recited for two reasons: the first is to celebrate the longevity of the book and its basic ideas. It has served as a guide for planning practitioners and students for over 50 years. Second, is the collaboration of the authors; a great object lesson in teamwork over a sustained period of time.