A Women’s History of Vatican I examines the controversies surrounding the First Vatican Council (1869–70) from the perspective of lay Catholic women who rejected papal infallibility. In an era of an allegedly feminized religion that considered women the church’s most obedient followers, prominent women proposed alternative models of ecclesiastical authority that were inclusive of the laity. My history of the council is both public and intimate: it addresses political and theological debate as well as the anguish felt by women who believed that their church was making a terrible error. Using the private papers and published writings of prominent Catholic women, I explore their strategies for finding a voice in the church and sustaining the tension between autonomous conscience and ecclesiastical demands for obedience.