Are companies, churches, and states genuine agents? Or are they just collections of individual agents that give a misleading impression of unity? This question is important, since the answer dictates how we should go about explaining the behaviour of these entities and whether we should treat them as responsible and accountable in the manner of individuals. Group Agency offers a new approach to that question and is relevant, therefore, in a range of fields from philosophy to law, politics, and the social sciences. Christian List and Philip Pettit take the line that there really are group or corporate agents, over and above the individual agents who compose them, and that a proper social science and a proper approach to law, morality, and politics have to take account of this fact. Unlike some earlier defences of group agency, their account is entirely unmysterious in character and, despite not being technically difficult, is grounded in cutting-edge work in social choice theory, economics, and philosophy.