World War I is an episode that illuminates the long-term change in definitions of women's authority from the nineteenth-century hegemonic concept of female moral authority to a latter-twentieth-century at least partial acceptance of women's professional and official authority on the basis of competence and rights. Historians of women have not examined often how gender has operated in the construction of authority in specific historical contexts, how gendered definitions of authority have changed, or how women have understood authority they have exercised. This article examines particular definitions of authority women adopted in three career fields during World War I: Young Women's Christian Association (YWCA) social workers, women police officers and patrols, and women industrial welfare supervisors. The central narrative focuses on the dramatic war's-end upheaval within the YWCA, which reveals a telling shift toward secularism in social workers' understanding of the mandate for their work. Calls for "modern," young YWCA workers were linked directly to notions that YWCA social work had become a paid career for trained women. Furthermore, for middle-class women seeking to prove their abilities and further their career possibilities, their relationships with working-class women formed an important basis for their self-justification. Studied together, these three expanding careers demonstrate women's blending of older and newer bases for their authority. While YWCA social workers increasingly introduced qualifications and methods of secular professionalism into an evangelical enterprise, women police and welfare supervisors drew upon older, religiously-based definitions of women's special nature to stake their claims in masculinist organizations.