While demand for international peacebuilding assistance increases around the world, the UN’s Peacebuilding Architecture (PBA) remains a relatively weak player, for many reasons: its original design, uneasy relations between the Peacebuilding Commission and Security Council, turf battles within the UN system, and how UN peacebuilding is funded. This chapter examines the PBA’s operations since 2005, against the evolution of the peacebuilding field, and discusses how the PBA can be a more effective instrument in the UN’s new “sustaining peace” approach. To do so, it would have to become the intergovernmental anchor for that approach, without undermining the intent that “sustaining peace” be a system-wide responsibility, encompassing the entire spectrum of UN activities in peace, security, development, and human rights.