This qualitative study explores academic librarians' perceptions of and experiences with information literacy assessment, focusing primarily on issues of professional identity, agency, and power. Findings from in-depth interviews reveal that instruction librarians view teaching as integral to their professional identity and use assessment to legitimize that identity, both personally and at the institutional level. While this suggests that assessment has the potential to elevate the status of librarians on campus, the interviews also highlight ongoing professional and organizational tensions that hinder assessment efforts and inhibit librarian agency. The authors recommend more transparent communication, among other strategies, to address these challenges.