The Centre d’histoire sociale du 20ème siècle (Center of 20th Century Social History) is a joint research unit between the Université Paris 1 and the CNRS (UMR 8058.) It was founded in 1966-1967 by Jean Maitron, with the support of Ernest Labrousse. Then, it was located in a small office at 16, rue de la Sorbonne. It was then called the Centre d’histoire du syndicalisme (Center of History of the Labour Movement.) One of the main distinguishing features of the center was the participation, from the beginnings, of the principal French Union Confederations (CFDT, CGT, CGT-FO, FEN and CNPF) to its board. This choice shows our desire to explore history, open to the collaboration with or confrontation with social movement figures. Ours is not an activist history, but one which has been enriched by this contact with activism. For forty years now we have maintained this ethic of history. The Center continues to work in connection with unions and, now, with a number of social and political forces, from associations to social or urban public powers, always with the same concern for mutual understanding with neither concessions nor compromises. The Center has also enjoyed, throughout the years, thanks to its successive directors, (Jacques Droz, Antoine Prost, Jean-Louis Robert, Annie Fourcaut, and Michel Pigenet) and to its longtime scientific secretary, Jacques Girault, a considerable development, especially in the last ten years. The number of researchers and associated professor-researchers has grown (from two in 1968 to five in 1975, nine in 1980, twenty in 2000 and now about forty researchers and associated professor-researchers.) Unfortunately, this growth was not matched by a similar growth in size of our administrative and technical teams, despite our move to a more modern space on the rue Malher. Starting in 1990, the Center has hosted the researchers of the CNRS of the GDR "Travail et Travailleurs," especially the team which publishes the large series of Dictionaries of the Labor Movement, the Maitron. The primary development of the Center has been, however, in its conception of its goal and in its research programs. From the Center of History of the Labor Movement it first became the Center of Historical Research on Social and Labor Movements then, in 1999, the Center of Social History of the 20th Century. The research programs it is carrying out, as an UMR (2010-2014) show the diversity of its orientations, all nonetheless linked through Social History. The State in Action, forms of socialization and social movements (frameworks, figures, and horizons,) systems of representation (in politics, in different systems), how to govern and live in a contemporary city – these form the four primary research topics of our program. Visitors of our website will see how the Center has followed, even initiated, many paths of innovative research, concerning, among other things, the relationship between individuals and the community, social groups and the structure and animation of society, practices, problems, and memory issues relating to labor, the social history of politics, the history of body, gender, and sexuality, migratory politics, city imagery, cultural history as social history of representations, and comparatism. Beyond its research role, the Center is also an important teaching organization. Two levels of education are offered, a Research Masters in the History of Contemporary Western Society, which has enjoyed great success, with more than 160 students enrolled in M1 and M2 (2008-2009). Every year, the Center hosts beneficiaries of research grants and its teachers currently advise almost 90 doctoral students, who all participate in a common seminar. Finally, the Center has an important collection of archives and documentation which testifies to the transversality of the research carried out in its laboratory and participated in by its exterior associates. In this way, it provides the public with a large library of social history, especially notable for its wealth of unpublished research (masters’ theses and doctoral dissertations,) and also for the many archival documents deposited by various activists and organizations. We are working towards modernizing these resources by digitizing our library and creating computer databases. We also work to cooperate with other centers of Social History archives.