In this new edition of a classic work -- now with a new preface -- on the roots of social scientific thinking, Immanuel Wallerstein develops a thorough-going critique of the legacy of nineteenth-century social science for social thought in the new millennium. We have to "unthink" -- radically revise and discard -- many of the presumptions that still remain the foundation of dominant perspectives today. Once considered liberating, these notions are now barriers to a clear understanding of our social world. They include, for example, ideas built into the concept of "development". In place of such a notion, Wallerstein stresses transformations in time and space. Geography and chronology should not be regarded as external influences upon social transformations but crucial to what such transformations actually is. Unthinking Social Science applies the ideas thus elaborated to a variety of theoretical areas and historical problems. Wallerstein also offers a critical discussion of the key figures whose ideas have influenced the position he formulates -- including Karl Marx and Fernand Braudel, among others. In the concluding sections of the book, Wallerstein demonstrates how these new insights lead to a revision of world-systems analysis.