This qualitative study explores how online learning is defined at academic libraries in the U.S. and examines the current roles and challenges of online learning librarians. Findings from in-depth interviews reveal that approaches to online learning in academic libraries vary in terms of audience and instructional strategies, and that online learning librarians perform several roles within the institution and often face challenges related to those roles. These findings suggest that while academic libraries have defined their approaches to online learning, the functional role of the online learning librarian should be clearly delineated and leveraged to support sustainable online learning initiatives at the institution. Based on these findings, the authors make recommendations for librarians and library administrators to support this evolving area of librarianship.