This study aims to investigate how professional social work is practiced in U.S. public libraries using a scoping review method. Following Arksey and O’Malley’s framework for conducting a scoping review, the research team undertook a scoping review of academic literature, such as peer-reviewed studies, academic conference presentations, and dissertations/theses, as well as so-called gray literature, including news articles and web search results. After every author’s review, a total of 53 materials were included in the review. The findings from this study provide evidence that collaborations between social work and libraries are documented in the academic and gray literatures, and the collaborations have been rapidly increasing since 2015. The findings also show that these collaborations tend to operate in three main ways: (1) professional social workers and social work interns directly working with library patrons, (2) professional social workers providing consultation with or training to library staff, and (3) social workers providing linkages between library staff and community-based social services agencies.