Our intention with this book is to extend the efficiency literature to the case of intertemporal models. We do this in steps. First, we introduce static network models which will serve as building blocks for our intertemporal budgeting models and our dynamic models. Next, we devote two chapters to productivity measurements, which we think of as comparative static models. Intertemporal budgeting models and dynamic models are taken up after that. Each chapter, except Chapter One, contains an empirical applica- tion. These applications are coauthored with colleagues and stu- dents; thanks are due to Runar Brannlund, Yijan He, Julius Hor- vath, Pontus Roos, Jerry Whittaker and S. (Lek) Yaisawarng . . We would also like to thank Dale Boisso and Kathy Hayes for gra- ciously sharing their data on Illinois municipalities with us. Two of the applications are already published, namely: “Environmental Regulation and Profitability: Applications to Swedish Pulp and Pa- per Mills,” Environmental and Resource Economics 6: 23-36, 1995, (Section 2. 5) and “Productivity and Quality Changes in Swedish Pharmacies,” International Journal of Production Economics 39: 137-144, 1995, (Section 3. 5). We are grateful to Kluwer Academic Publishers and Elsevier Science for kindly allowing us to reproduce these publications here. During the summer 1995 we spent a very enjoyable two months at the Center for Economic Studies (CES) at the University of Munich.