This volume contains Kalecki's writings on the theory of growth of a socialist economy and the theory of economic efficiency of investment. These are supplemented by essays on some economic and social problems of People's Poland. Though quite theoretical in nature, both the Introduction to the Theory of Growth in a Socialist Economy and Kalecki's many studies in the theory of economic efficiency of investment projects are deeply rooted in his practical experience as an economic planner. It is only in this light that the significance of his contributions to the theory of economic efficiency of investments can be assessed, and his ideas on socialist reproduction can be seen as a whole. Its central point is economic planning, which for Kalecki was the fundamental feature of a socialist economy.