The United Nations Peacebuilding Commission (PBC) was established in December 2005. Its emergence was the culmination of a long and contentious process, stretching back to at least the early 1990s. Robert Jenkins traces the origins and evolution of peacebuilding as a concept, the creation and functioning of the UN Peacebuilding Commission as an institution, and the complicated relationship between these two processes. Centred on two closely related questions, he examines: how has continued contestation over what exactly peacebuilding is, and how its objectives can most effectively be achieved, influenced the institutional design and de facto functioning of the PBC? to what extent has the work of the Commission, during its first two years in existence, helped to shape how various actors conceive of and seek to operationalize the notion of peacebuilding?