This volume presents the proceedings of ECSCW 2011, the 12^th European Conference on Computer Supported Cooperative Work. Each conference offers an occasion to critically review our research field, which has been multidisciplinary and committed to high scientific standards, both theoretical and methodological, from its beginning. The papers this year focus on work and the enterprise as well as on the challenges of involving citizens, patients, etc. into collaborative settings. The papers embrace new theories, and discuss known ones. They contribute to the discussions on the...