In 2018, Jair Bolsonaro’s election as president of Brazil, followed by his appointment of numerous military officers to his cabinet, initiated a period marked by the deterioration of the quality of the country’s democracy, a pattern also observed in several other democracies, old and new. This book investigates cabinet militarization in democratic regimes, highlighting why presidential systems often see a higher presence of military personnel in cabinets than parliamentary or semi-presidential executive types. Leaders who pursue this route are often characterized by extremist ideologies and found in countries with low or declining levels of party system institutionalization. Focusing on Brazil, but always with a comparative perspective, the book examines the historical, institutional, and political context of cabinet militarization. By combining cross-national data and a detailed case study, the book aims to uncover the causes of that variable, the challenges it poses to democratic governance, and its impact on defense policymaking.