What is the difference between a mercenary and a state soldier? The answer is not nearly as intuitive as it might appear at first glance. Drill deeper, to the normative questions, and the picture becomes even less clear. What is the moral difference between privately enacted war and publicly enacted war? The morality of private war presents one of the most sustained recent treatments of this question. James Pattison's contribution is part of a broader research programme on the ethical dimensions of non-state actors in conflict, including mercenaries, private military firms and pirates. He approaches the issue by addressing what, for some, is an uncomfortable analytical feature of private force: it is rather difficult to ascertain anything intrinsically wrong about warfare carried out by private contractors. As some scholars have noted in recent years, moral arguments against private military actors apply, to a significant degree, to state militaries as well. Pattison is concerned with two principal issues: the permissibility of private military force and whether private military force is preferable to public force. In this sense, his inquiry taps into the very old tradition of just war theory, in the context of a new phenomenon. Of course, commercial force for hire has been a part of warfare for most of history, but its emergence as a legal, transnational, corporate enterprise over the past two decades has brought its ethical implications into very sharp relief.