Breaking Protocol tells the story of the first female ambassadors in US history (1933–1964): Ruth Bryan Owen, Florence Jaffray Harriman, Perle S. Mesta, Eugenie M. Anderson, Clare Boothe Luce, and Frances E. Willis. This is the first group biography of the Big Six, one that places these women in a wider historical context based on deep and broad research in archival sources. It restores these women to their rightful place in history, and it assists the larger project of rendering women in international history visible. It begins by establishing the historical context, the male-dominated world of American diplomacy in the first half of the twentieth century. It then devotes one chapter each to the six female ambassadors, describing their backgrounds and appointments, analyzing the issues they faced and experiences they had on the job, and assessing their performances. It also traces the ambassadors’ reception by host countries; their sometimes fraught relations with the male-dominated State Department; the press coverage they received; the complications of protocol and the spouse issue; and how they practiced “people’s diplomacy”—getting to know, and representing America to, the host country’s whole society, not just its ruling elite. It ends by outlining the progress made and obstacles faced by women since the mid-1960s, and it concludes that, through their successful performances, the Big Six significantly contributed to gender progress in US foreign relations.