Marco Giugni is a researcher at the Department of Political Science at the University of Geneva. He has authored or coauthored several books and articles on social movements. He is the author of Entre stratégie et opportunité (1995), coauthor of New Social Movements in Western Europe (1995) and Histoires de mobilisation politiques en Suisse (1997), and coeditor of From Contention to Democracy (1998) and How Social Movements Matter (1999). His current research focuses on mobilization over ethnic relations, citizenship and immigration in a cross-national comparative project (MERCI). Florence Passy is assistant professor at the Department of Political Science at the University of Geneva. She has written extensively on social movements and political participation. She is the author of L’action altruiste (1998) and coauthor of Histoires de mobilisation politiques en Suisse (1997). Her current research focuses on mobilization over ethnic relations, citizenship and immigration in a cross-national comparative project (MERCI).