Joint action is pervasive among us. We carry a piano upstairs, dance the tango, paint a house together, go for a walk together, and prepare hollandaise sauce together. Joint action is also something we value or care about—both intrinsically and instrumentally. We enjoy going for a walk together and preparing hollandaise sauce together; and we carry a piano upstairs together and paint a house together because we find it difficult to achieve the intended results on our own. But what is it for us to act together? Philosophers agree that joint action is not simply an aggregation of acts by individuals, however coordinated. People can be acting individually in a coordinated way—acting in parallel, as we might say—but still not be acting jointly in a proper sense. The difference is often illustrated by reference to contrast cases (Tuomela and Miller 1988; Searle 1990; Gilbert 1992, 2000; Bratman 2006, 2014). Consider one suggested by Michael Bratman (2006). Imagine that you and I are walking together down Fifth Avenue. Now contrast this with a case in which I am walking down Fifth Avenue alongside a stranger and in which the stranger and I are walking at the same pace, without bumping into each other. Both cases involve a sequence of individual, coordinated acts. Yet, it is intuitively clear that the case of you and I walking down Fifth Avenue constitutes an instance of joint action, while the case of my walking alongside a stranger does not. It is usually inferred from this that the mark of joint action does not reside solely in its external or behavioral component. It resides also, and more fundamentally, in its internal component, in the participants’ having a shared (or collective or joint) intention to so act.