Historically, men have been more likely to be appointed to governing cabinets, but gendered patterns of appointment vary cross-nationally, and women's inclusion in cabinets has grown significantly over time. This book breaks new theoretical ground by conceiving of cabinet formation as a gendered, iterative process governed by rules that empower and constrain presidents and prime ministers in the criteria they use to make appointments. Political actors use their agency to interpret and exploit ambiguity in rules to deviate from past practices of appointing mostly men. When they do so, they create different opportunities for men and women to be selected, explaining why some democracies have appointed more women to cabinet than others. Importantly, this dynamic produces new rules about women's inclusion and, as this book explains, the emergence of a concrete floor, defined as a minimum number of women who must be appointed to a cabinet to ensure its legitimacy. Drawing on in-depth analyses of seven countries (Australia, Canada, Chile, Germany, Spain, the United Kingdom, and the United States) and elite interviews, media data, and autobiographies of cabinet members, Cabinets, Ministers, and Gender offers a cross-time, cross-national study of the gendered process of cabinet formation.