In the public administration literature, the concept of co-production has developed under the influence of the participatory democracy narrative and has also been strongly influenced by the New Public Management. This chapter discusses the important conceptual developments made within this broad literature and argues that co-production has been positioned mainly as an optional extension of the public service production process. Here, the emphasis is on the voluntary and active partnership of citizens (as individuals or in groups) during the design and delivery of public services. The rationale for co-production, from this perspective, is around its potential to create value by increasing the number of actors who can contribute to tackling difficult and cross-cutting social problems. Importantly, co-production is also forwarded as a means of improving democracy through increased participation. However, this chapter also considers the various barriers and challenges to co-production, such as tokenistic involvement and unequal power relations.