In social sciences researches, as in urban life, citizenship is « back in town ». From one side to the other of the Atlantic ocean, citizenship appears to be the obsessional paradigm of urban policies and politics. Its renewal is partly founded on recent public actions in devasted neighborhood and on new metropolitan planning process. But the question also deals with local power and with new emergent identities and political subjects. For 20 years, globalization and migratory movements have reshaped the traditional conception of citizenship, making its come-back on the urban scene possible. In this context, new forms of citizenships are rising: eco-citizenship, urban and cultural citizenship, ethnocitizenship... making citizenship an undefined ideal for today modern democracy. Regarding citizenship in cities with a comparative approach between Europe and Americ(s), the purpose of this conference is to open new ways for further researches ligthning today mecanisms, social and political changings and forces in action.