This article is the third and last of a multi-part study on academic instruction librarians' conceptions and experiences of teacher agency in relation to their instructional work. Based on the findings of an online survey of academic instruction librarians, this final article concentrates on the role that librarian relationships play in academic instruction librarians' conceptions and experiences of teacher agency. The findings illustrate the importance of supportive workplace cultures and workplace relationships in instruction librarians' capacities to enact individual and collective agency in their instructional roles. The findings have implications for instruction librarians and library organizations that endeavor to foster workplaces in which instruction librarians are valued and supported by one another and by their institutions.