This volume and a subsequent one, contain several new papers on index number and aggregation theory, as well as some previously published papers, by W.E. Diewert and co-authors. The two volumes study aggregation problems in economics, primarily the aggregation over goods problem. However, some of the chapters also touch on aspects of the aggregation over agents problem. In the present volume, the reader can find, according to his/her requirements, either a short course on index number theory; a more in-depth course; or chapters on specific topics such as the measurement of inequality, functional forms for social welfare functions, or the theory of choice under uncertainty. Students and researchers will appreciate having these papers easily accessible. The book will be valuable too for those in the government agencies around the world that produce price statistics, insuring an understanding of important properties of alternative indexes, and of how economists use and interpret price indexes.