The baby trains were the hallmark of a Catholic placing-out program begun in the 1870s by the Foundling Asylum of the Sisters of Charity, later known as the New York Foundling Hospital. The program extended and modified the Protestant orphan train movement by sending abandoned youngsters to live among pious Catholic settlements along the western frontier of the United States. At once ingenious and fraught with risks, the baby trains reflected the Foundling's multifaceted mission to rescue homeless children while bolstering Catholic culture—in the form of beliefs, values, and practices—against the persistent threat of proselytizing, Protestant charities. The face of this movement in recent scholarship has been the Children's Aid Society; the Foundling has been treated as an offshoot rather than an innovator in its own right. This essay examines both the logistics of the baby train program and its significant influence in modernizing the placing-out movement. This research tests historiographical assumptions about the dynamics of Catholic culture after the Civil War, the importance of religious institutions for enabling ethnic persistence within frontier enclaves, the role of child welfare work in perpetuating religious culture, and the work of women in reproducing that culture in future generations. The baby trains are an important chapter in the fortification of sectarian Catholicism in the mid-nineteenth century, as well as the history of faith-based, social welfare in America.