This book contains fourteen of Professor Domar's principal papers, beginning with On the Measurement of Technological Change, published in 1961 and ending with The Blind Men and the Elephant, which has not appeared in print before. The book is divided into four parts. Part I presents three non-technical essays on economic development and economic systems, including a novel comparison between them. Part II deals with the theory and measurement of the so-called "Index of Total Factor Productivity" for several countries, and includes an essay on the theory of index numbers. Part III compares the Soviet and American patterns of economic development. Part IV presents three applications of economic theory to historical problems: in particular, serfdom and slavery, and contains the now classic essay The Causes of Slavery or Serfdom.