A dedication to service is often cited as a hallmark of a profession. Service is included as one of eleven Core Values in the American Library Association’s “Core Values of Librarianship” (2004). For librarians, service includes helping people find information resources to meet their educational, recreational, and work needs. Reporting findings from a larger study into the professional identity of librarians, this paper explores the centrality of service, with specific attention to how librarians advocate for their services and, ultimately, for librarianship. Using a discourse analysis approach, this study examines the roles that Service as a Core Value and advocacy play in the construction of professional identity. Three different data sources were used: professional journals, e-mail discussion lists, and research interviews. The data were analyzed for the discourses librarians use when describing librarians, librarianship, and professionalism and their connection to advocacy. When librarians advocate for the services they offer, they are in fact advocating for the value of the profession. Discursively, speaking or writing about advocacy positioned librarians as active participants in their own identity formation. By making advocacy a central activity of the profession, librarians not only challenged others’ perception of librarianship, they challenged their own understanding as well.