The proliferation of private security services has become a matter of some concern because it highlights on the weakness of public security institutions and occurs together with an increase in crime. This book develops an alternative analytical model based on an historical and institutional approach. While focusing on the case of Guatemala, it argues that private security is an outcome of political and social processes with a strong historical dimension in which the trajectories of state security institutions are fundamental explanatory dimensions. Both commercial private security firms and non-commercial citizen security organizations interact with processes of institutional change within political contexts in continuous flux. Based on an extensive use of historical empirical sources and interviews, the book identifies causal mechanisms and explains private security proliferation in terms of path dependent processes.