In Early Modern Europe, mercenary armies were the norm. With the rise of the state military, mercenaries seemingly disappeared, but private security has reemerged since the end of the Cold War. In many discussions of this phenomenon, privatization is seen as a policy choice undertaken by 'bad' leaders and as a sign of state failure. To evaluate these claims, however, requires a more objective investigation of the conditions under which leaders in weak states choose to privatize. This dissertation seeks to answer the following two questions: (1) under what conditions are states most likely to hire privatize military services, and (2) how can we predict which services will be privatized? I argue that dysfunctional civil-military relations, reliance on appropriable natural resources, and civil conflict all increase the likelihood that a regime leader will hire PMCs. I also argue that existential threats to the regime from the military (via dysfunctional civil-military relations) or rebels (via civil conflict) drive leaders to privatize at the tip of the spear. Evidence from original quantitative and qualitative data on security privatization in sub-Saharan Africa from 1990-2010 supports my theory.