Mercenary soldiers are an historical constant. The emergence in the last two decades of a ‘new’ type of ‘mercenary’ – the private security contractor – has been portrayed as a feature of contemporary warfare, reflecting their acceptance by states into the international security framework. Distinctions are drawn between mercenaries and private contractors, with the latter being depicted as a post Cold War phenomenon, where demands for protection from weak states are met by ‘private armies.’ Key concerns with private contractors are their access to the use of force, notionally a preserve of the state, and their capacity to operate unregulated, without state control. Critics argue that state inertia towards regulation facilitates the privatisation of warfare. The purpose of this thesis is to examine the relationship between private security contractors and states; in particular, the origins and mechanisms that allow private entities to operate, without regulation. Private contractors are conceptualised as a tool to extend state interest, a potentially dangerous security resource which requires a risk management approach by states. The question, of how states risk-manage private security actors, has framed the research. This question is underpinned by enquiries into the nature of the relationship between states and private security contractors, the options available to states to retain control, and how these mechanisms operate in the private/public domain. A meta-review of the literature has been undertaken, with qualitative analysis of primary and secondary source data, and selective use of statistical information. Source texts include international security, military history, risk, state-organised crime and analyses of the mafia.