The increased use of private military and security companies (PMSCs) is often said to be one of the most significant changes to the military in recent times. The Morality of Private War: The Challenge of Private Military and Security Companies provides a detailed assessment of the moral arguments for and against the use of PMSCs. In doing so, it considers objections to private force at the employee, employer, and international levels. For instance, does the potential for private contractors to possess mercenary motives affect whether they can use military force? Does a state abdicate an essential responsibility when it employs PMSCs? Is the use of PMSCs morally preferable to the alternatives, such as an all-volunteer force and a conscripted army? What are the effects of treating military services as a commodity for the governing rules of the international system? Overall, The Morality of Private War argues that private military force leads to not only contingent moral problems stemming from the lack of effective regulation, but also several deeper, more fundamental problems that mean that public force should be preferred. Nevertheless, it also argues that, despite these problems, PMSCs can sometimes (although rarely) be morally permissibly used. Ultimately, The Morality of Private War argues that the challenges posed by the use of PMSCs mean that we need to reconsider how military force ought to be organized and to reform our thinking about the ethics of war and, in particular, Just War Theory.