This article investigates the sources of foreign ministries’ policy-making capacity in presidential regimes. Using the concept of family resemblance, we argue that professionalization of the diplomatic corps is a necessary condition, whereas the institutional attributions of the ministry and the degree of presidential delegation are relevant but substitutable elements. The higher the scores on either of the latter dimensions, the stronger is the capacity of the foreign ministry to influence the chief executive and to contest other players’ policy preferences. To empirically validate our concept, we measure the three dimensions in Argentina, Brazil, and Mexico between 1946 and 2015 using data on diplomats’ recruitment and career paths, influence of diplomatic schools and doctrines, appointment patterns of foreign ministers, and relevance of presidential diplomacy, with an emphasis on travels abroad. Our analysis indicates that Argentina, Brazil, and Mexico enjoy a high level of professionalization of their diplomatic corps; however, differences—both across countries and over time—remain regarding institutional attributions and presidential delegation.