Over the past several years, there has been an expansion in the use and awareness of open educational resources (OERs) in postsecondary institutions in the United States. Some states have invested funds to expand the use of OERs across their campuses as an alternative or supplement to traditional course materials that students typically pay for out of their own pocket, but also as materials that can be updated expediently to keep up with new technologies. Some of these initiatives have been driven by state agencies of higher education and system offices, while others have taken a grassroots approach, usually developed at individual campuses. To gain a better understanding of the sustainability of OER initiatives, this study first reviews existing literature on the implementation and sustainability of OER programs and initiatives, with the goal of developing a holistic framework to assess their impact and understand the challenges they face. To further investigate, Ithaka S+R employed a case study methodology focusing on four postsecondary state agencies or systems and a selection of their institutions, conducting three interviews per state, for a total of 12 interviews. Key findings include: (1) there is no one-size-fits-all model for how OER initiatives are sustained; (2) OER initiatives flourish when they align with institutional priorities and are framed as a tool that can address several goals beyond affordability, such as advancing equity, access, or instructional innovation; (3) academic libraries are central nodes in OER champion networks; (4) awareness of and enthusiasm for OERs are increasing in our case study states, but the devil is in the details; and (5) ensuring that OERs reflect the diversity of student populations is crucial in fostering student engagement and academic success.