This book aims to train students and early professionals in the use of computer models for policy analysis, with special emphasis on economics, and some emphasis on demography and energy issues. The author reviews basic forecasting theory; the limits and uses of forecasting; and the recent history of forecasting, econometrics in particular. The book facilitates hands-on learning: the model and its background is described and then the reader is taken through the model step-by-step so that with the completion of each chapter he or she actually carries out a run of the model.