Many of the things we do, we do together with other people. Think of carpooling and playing tennis. In the past two or three decades it has become increasingly popular to analyze such collective actions in terms of collective intentions. This volume brings together ten new philosophical essaysthat address issues such as how individuals succeed in maintaining coordination throughout the performance of a collective action, whether groups can actually believe propositions or whether they merely accept them, and what kind of evidence, if any, disciplines such as cognitive science andsemantics provide in support of irreducibly collective states.The theories of the Big Four of collective intentionality - Michael Bratman, Raimo Tuomela, John Searle, and Margaret Gilbert - and the Big Five of Social Ontology - which in addition to the Big Four includes Philip Pettit - play a central role in almost all of these essays. Drawing on insights froma wide range of disciplines including dynamical systems theory, economics, and psychology, the contributors develop existing theories, criticize them, or provide alternatives to them.Several essays challenge the idea that there is a straightforward dichotomy between individual and collective level rationality, and explore the interplay between these levels in order to shed new light on the alleged discontinuities between them. These contributions make abundantly clear that it isno longer an option simply to juxtapose analyses of individual and collective level phenomena and maintain that there is a discrepancy. Some go as far as arguing that on closer inspection the alleged discontinuities dissolve.