To effectively support research activities and data stewardship, library and information professionals engage in collaborative projects that involve diverse disciplinary and institutional partnerships. While this idea is stressed in existing literature, the different ways in which librarians and domain experts working in library and information organizations engage in collaboration is rarely made explicit. This paper proposes the term library-mediated collaborations to capture the ways in which library and information professionals perform actions that facilitate, coordinate, and even create opportunities for multiple stakeholders to leverage their resources and expertise in data curation. By mediation, the paper refers to the active and critical involvement of institutional actors, in this case information professionals in a national library, in ensuring the creation and execution of a project over a period of time. The paper discusses the various manifestations of library-mediated collaborations in four data cu-ration projects currently taking place at the National Agricultural Library (NAL). A national library located within the United States Department of Agriculture (USDA), NAL has long supported the preservation of and access to agricultural information. The paper concludes by identifying important questions that information professionals may consider asking when they participate in collaborative data curation projects.