The sixth volume of the Collected Works of Michał Kalecki, one of the twentieth-century's pre-eminent economists, contains his empirical studies of the capitalist economy, published primarily in pre-war Poland.The first part of the book collects together reviews of business conditions in commodity markets, studies of the structure and operations of large companies and cartels, and articles on international economic relations. These studies, written between 1928 and 1935, demonstrate Kalecki's keen insight into the international consequences of the Great Crisis of 1929-33, and into the developments in Nazi Germany. The second part contains Kalecki's papers on the methodological problems of examining business fluctuations and on constructing indicators of economic trends. Part 3 comprises, Kalecki's estimates (together with Ludwik Landau) of the national income in Poland and of its structure. These studies, conducted between 1931 and 1935, were unique at the time in taking into account the distribution of aggregate income between the main social classes.The editorial notes and annexes at the end of the volume not only provide invaluable background information and explanatory glosses on the main text, but also give invaluable insights into the development of Kalecki's thought.