The OECD considers co-production an important social innovation. This paper discusses alternative definitions of innovation, since traditional definitions, employed by economists for industry and manufacture, do not fit well with public service provision. It then presents some definitions of co-production, discusses the relationship between staff and their clients, and asks whether co-production is based on individual acts, collective action or both. It briefly discusses several factors that can contribute to making coproduction more sustainable. This paper concludes that governments should develop more flexible, service specific and organization specific approaches for promoting co-production, rather than looking for simple “one size fits all” solutions to the challenges facing public service delivery in the 21st Century, particularly for enduring welfare services. Finally, it recommends more research to promote sustainable co-production.