Useful lessons can be drawn from international involvement in development and peacebuilding in Aceh, 2005–2006. Over this period, Aceh emerged from decades of internal conflict through a peace agreement between the Government of Indonesia and the Free Aceh Movement (or GAM). Although political shifts across Indonesia are widely accepted as the main reason why the agreement has held to date, international bodies played valuable supporting roles in brokering talks, monitoring progress, and providing development aid. This paper builds on ground-level experiences of what worked and what did not, finding that the process of devising and implementing international interventions confronted various barriers, including: limited scope for international actors to affect critical, domestic conditions; divergent interests and incentives that international agencies responded to; and institutional limits and constraints on what those international agencies could deliver. The most effective interventions in Aceh built on agencies' core strengths rather than aiming to implement global ‘best practice’, and forged relationships with domestic interests. It is suggested that understanding of these ground realities is not always evident in international policymaking, and greater recognition would help improve peacebuilding interventions in future.