Peer support may improve self-management among the millions of people with diabetes around the world. A major challenge to international promotion of peer support is allowing for tailoring to population, cultural, health system and other features of specific settings, while also ensuring congruence with standards for what peer support entails. One strategy to address this challenge was used in the Robert Wood Johnson Foundation Diabetes Initiative. Key functions of self-management-Resources and Supports for Self-Management-were identified. Individual programmes were then encouraged to implement these resources and support in ways that were feasible in their settings and responsive to the needs and perspectives of those they serve. Extending this to peer support, three Key functions are (i) assistance in managing and living with diabetes in daily life; (ii) social and emotional support and (iii) linkage to clinical care. International promotion may be advanced by emphasizing these key functions and then encouraging local variation in the specific ways they are addressed. Similarly, evaluation of the general benefits of peer support across several individual programmes may rest on measurement of implementation of the key functions, participants' reports of receipt of them and common end points. Challenges to promoting peer support include integrating peers amidst others in the health care system, harmonizing peers with family and other social networks, maintaining the engagement of peer supporters and those they assist and preventing training, quality improvement and professionalism from distorting the fundamental benefits of support from a peer.