Appraisal and selection are key activities necessary for the responsible stewardship of research data. Not all data has long-term research value, and the increasing volume of data produced and published to meet short- and mid-term needs creates a burden on both the repositories storing and maintaining access to the resources and the researchers searching for quality data. Repository appraisal practices, often carried out as part of the curation process at the time of deposit to optimize data for sharing and reuse, need to better address the long-term sustainability of FAIR data practices. This guide is designed to be used alongside a repository’s existing acquisition, collection development, preservation, and deaccessioning policies and other high-level institutional strategy documents to help curators work with researchers and preservation specialists to evaluate research data for long-term preservation.