How are formal rules and informal norms for appointing cabinet ministers gendered? What combination of formal process and informal practice serves to facilitate (or inhibit) the appointments of women to cabinet posts? In principle, within a single political system, formal rules apply equally to every cabinet appointment; nonetheless, formal rules that appear neutral on their face often have gendered impacts (and have gendered origins). Informal norms may be more likely to vary – over time, and by party and specific ministry – and hence may have a greater impact on the process and practice of appointing cabinet ministers, and may have a more strongly gendered impact on women’s cabinet appointments, both positive and negative. To the extent that informal norms are invisible (or visible and known only to political insiders), norms may gender formal rules to women’s disadvantage; to the extent, however, that informal rules are susceptible to change as a result of pressure and influence from organized women, both inside and outside the political party of a prime minister, norms may be recast relatively quickly to women’s advantage. This paper examines cabinet appointments in three parliamentary democracies – Spain, Sweden, and the United Kingdom; identifying formal appointment rules in each country; and maps informal norms to the major left and the major right party in each country. The paper develops hypotheses about the intersection of specific formal rules and informal norms to identify context opportunities for explaining and predicting changes in women’s appointments to cabinets.