This dissertation examines the travelers' aid movement of the late nineteenth and early twentieth centuries through a case study of the Travelers' Aid Society of New York. Travelers' aid was part of a larger movement for moral reform that arose as a response to social problems unleashed by industrialization, urban growth, and mass immigration. Moral reformers believed that vices such as prostitution were wreaking havoc on individuals, communities, and, consequently, on the national fabric. To combat prostitution, reformers launched a variety of campaigns in both the United States and Europe, one of which targeted a practice known as "white slavery," i.e. the coercion of European and Euro-American ("white") women into prostitution. The Travelers' Aid Society of New York (TAS) was founded in 1907 as an anti-white slavery organization. Its mission was to prevent female travelers from falling victim to white slavery by providing social work to them at train stations and piers. Female agents of the TAS searched for disoriented travelers (immigrant and native-born, working- and middle-class) in the hopes of reaching them before they were in any immediate danger. Agents escorted travelers to a variety of locations, including affordable lodging facilities; provided them with resources such as food; and gave assistance in finding employment. Agents also helped travelers navigate through New York's complex transportation system. This study of the TAS supports an interpretation of social welfare that integrates two fundamental, often competing, concepts: discipline and empowerment. I argue that the TAS's disciplinary elements were moderate, which allowed it to frequently act as a productive mediator between travelers and their new environment. This was especially true during the TAS's period as a women's organization, 1906-1910. We see more evidence of discipline in the ensuing period when the TAS transitioned to a mixed-sex organization led by men and its anti-white slavery activism became more pronounced. The TAS, like most of its contemporaries, exaggerated the threat of white slavery, which led to instances where agents were overaggressive in their handling of cases involving female travelers and unknown men. However, its emphasis on white slavery should not obscure the prevalence of crime at the city's transportation hubs. Subsequently, TAS vigilance also thwarted criminal attempts on women's bodies and property.