This book includes the results of an International Workshop held at the Department of Political Economy of the University of Siena in December 1986. It focuses on the presentation, discussion, and comparison of two most interesting theories proposed for the explanation of long waves, namely the technological (neo-Schumpeterian) and the "social" approach. One of the main results that emerges is that the two approaches are not mutually exclusive and that an integrated theory of long waves is a feasible construction. The book consists of three parts. The first comprises theoretical approaches including also contributions shaped in the neo-Marxist and neoinstitutional perspectives. In the second part, applied analyses are gathered, ranging from case studies to econometric works on both underdeveloped and industrialized countries. Finally, contributions on economic history, methodological aspects and history of economic doctrines are also presented.