Most work at the intersection of law and the philosophy of action focuses on criminal responsibility. Unfortunately, this focus has been at the expense of reflecting on how the philosophy of action might help illuminate our understanding of issues in civil law. In this essay, focusing on Anglo-American jurisprudence, we examine the conditions under which a party to a legal agreement is deemed to have the capacity required to be bound by that agreement. We refer to this condition as the (...) capacity condition. We begin by showing how recent work on the metaphysics of powers might ground an account of the role of capacities in the metaphysics of intentional agency. After discussing the capacity to contract in Anglo-American jurisprudence, we show how the general ontology of capacities and agency sketched can ground and help clarify legal thinking about capacity. We argue that when we couple our understanding of capacity with relevant recent data from developmental neuropsychology, a lacuna in Anglo-American contract law becomes evident. Specifically, it appears that persons in early adulthood do not clearly satisfy the conditions requisite for them to satisfy the capacity condition. In the light of this, we sketch some potential solutions that are compatible with existing legal standards and would contribute to a more consistent application of the capacity condition in contract law. (shrink)