Professor Michael Bratman (Stanford University) gives the 8th Routledge Lecture in Philosophy. Human beings act together in characteristic ways, and these forms of shared intentional and shared cooperative activity matter to us a great deal. Think of friendship, singing duets, and the joys of conversation. And think about the usefulness of conversation and of how we frequently manage to work together to achieve complex goals, from constructing buildings to putting on plays to establishing important results in the sciences. I seek a framework for understanding these basic forms of sociality. And the conjecture I explore in this talk is that structures of individual planning agency are at the heart of such sociality. Lecture sponsored by Routledge. Recorded Thursday 12th June 2014.