Schumpeter is without doubt one of the most influential economists of the 20th century. Business Cycles [1939] is considered his great work. We reprint the first edition published in 1939 in two volumes. In "Business Cycles" Schumpeter focuses powerfully on the historical role of technological innovation in accounting for the high degree of instability in capitalists societies. He aims to analyze empirically the actual process of economic development using historical and statistical material based on the theoretical framework he developed in earlier writings. He tried to integrate theory and history primarily by means of statistics. It is because he adopted the method of filling in the statistical contours with detailed industrial history that "Business Cycles" comprises two large volumes. A Classic work, not otherwise available in the original two volume format.