This book investigates when and why governments in advanced democracies deploy armed forces for domestic security. It develops a theoretical framework conceptualising military policing as a policy instrument and identifies circumstances that lead governing parties to choose military over police for law-and-order agendas. The analysis reveals that armed forces are often favoured because they can be deployed more rapidly and at lower cost, arguing that military deployments frequently respond to economic convenience and become particularly attractive under fiscal constraint. The framework is tested on Italy, Europe’s heaviest user of armed forces for domestic security, drawing on extensive empirical evidence, including over 50 interviews with military officers, politicians, and police officials, as well as parliamentary debates and press sources. The book includes exploratory analysis assessing the framework’s applicability to other European states. Unlike existing studies focusing largely on Latin America, this work offers one of the first comprehensive analyses of causal factors driving military policing in advanced European democracies, making a significant contribution to civil–military relations scholarship. This volume will interest scholars, students, and practitioners of military studies, civil–military relations, policing, and security studies, as well as think tanks and policymakers seeking to understand the political dynamics behind domestic military deployments.