This article describes the National Park Service's (NPS) progress in an ongoing effort to develop museum collection significance criteria for its geology, paleontology, biology, archeology, ethnography/ethnology, history, and archival collections. The goal is to create sets of significance criteria that are practical, flexible, recognize the associative value of the NPS's collections, and provide continuity and context for the stewardship of collections over time. Effective significance criteria will increase the intellectual understanding of collections; inform and record collection acquisition and deaccession; and assist in management decisions related to collections. This is an immense undertaking complicated by differences among disciplines and a large geographic scope. The significance criteria effort requires agency support through a national staff coordinator and funding for the final development and implementation phases.