Contributor(s): Professor Immanuel Wallerstein | Immanuel Wallerstein (@iwallerstein) is Senior Research Scientist in Sociology at Yale University. He is the former President of the International Sociological Association (1994-1998), and chair of the International Gulbenkian Commission on the Restructuring of the Social Sciences (1993-1995). He writes in three domains of world-systems analysis: the historical development of the modern world-system; the contemporary crisis of the capitalist world-economy; the structures of knowledge. Books in each of these domains include respectively The Modern World-System (4 vols.); Utopistics, or Historical Choices for the Twenty-first Century; and Unthinking Social Science: The Limits of Nineteenth-Century Paradigms. Craig Calhoun (@craigjcalhoun) is Director of the London School of Economics and Political Science.