Success in open educational resources (OER) has been reported by the Massachusetts Institute of Technology in the USA and the Open University in the UK, among others. It is unclear, however, how valuable OER are in learning and teaching. Approaches to OER policy and sustainability are just two other key aspects that remain unresolved across the sector. Based on the findings from the Open, Transferable, Technology-enabled Educational Resources (OTTER) project at the University of Leicester, UK,1 we introduce the OER mix framework: purpose, processes, product, and policy. We argue that different mixes of the four Ps can generate different approaches to OER. We discuss the relevance of the framework and its importance for social inclusion and widening access to higher education. We also discuss the implications of the OER mix for the openness agenda. Institutions may find value in adapting and applying the framework. We invite colleagues to critique it and report back. (Contains 9 notes, 7 tables and 1 figure.)