This book investigates the connection between tightening mobilization constraints and the use of PMSCs in the United States, the United Kingdom, and Italy. Drawing on neoclassical realism and institutionalist theory, it conceptualizes democracies’ use of private military and security companies (PMSCs) as an attempt to circumvent the tightening constraints on the mobilization of military power. The use of private military contractors is less subjected to parliamentary restrictions and less visible to public opinion than the deployment of soldiers. Rather than cheaper in financial terms, PMSCs are therefore politically cost-effective, as they enable decision-makers to minimize the institutional obstacles on conducting military operations and the electoral costs attached thereto. The need to reduce the ex ante hurdles and the ex post costs of military deployments fills the blind spots of alternative explanations for the use of PMSCs based on effectiveness, ideology, and organizational interests.