This book aims to kill two birds with one stone. On the one hand, the destabilising rise in the number and power of private military companies. On the other, the failure of the international community to provide adequate solutions to new peacekeeping dilemmas. I begin by pinning down private military companies in international law: Are they mercenaries? What laws, if any, restrain them? Are these laws enforced and if not, why not? The second part asserts States' responsibility for these companies, whilst revealing that most States either cannot or simply will not step up to this responsibility. Finally, I introduce our second dilemma: the UN's failures in peace enforcement. I suggest that the reasons for these failures lie in factors that are not present when dealing with private military companies. Therefore, to address the issues of unrestrained private military companies and unsatisfactory peacekeeping operations, I suggest the registration, monitoring and use of private military companies solely by the United Nations for peace enforcement initiatives. I offer a practical plan for this suggestion, as well as a section on anticipated counter-arguments and critiques.