The Regis Lay Apostolate was a pioneering postgraduate lay volunteer program that grew out of the heyday of Catholic Action and the lay apostolate in the mid-century American church. The program operated out of Regis College, an all-female school run by the Sisters of St. Joseph in Weston, Massachusetts. Under the vision of Sister Mary John Sullivan, the program ran from 1949 through 1972 and sent approximately 225 Regis graduates to serve at Catholic mission schools domestically and internationally. Sister Mary John and the Regis volunteers played an important role in spearheading and shaping a larger movement of postgraduate Catholic lay volunteers. This phenomenon remains a vibrant force in American Catholicism today, but has gone largely unstudied. As such, exploring the Regis Lay Apostolate as well as the motivations and experiences of its volunteers provides an important first step towards understanding the emergence, development, growth, and impact of the Catholic postgraduate volunteer model, and where it fits within the greater narratives of both Catholic American history and twentieth-century American volunteerism.