This document announces a side event to the UN High-level Thematic Debate on Peace and Security. The event will discuss how cooperation between the UN, regional organizations, and civil society can strengthen the global peacebuilding architecture. It notes that while the UN has recognized the importance of these actors, cooperation remains limited. The event aims to share lessons on inclusiveness and make recommendations to build strategic partnerships between the UN, regional groups, and civil society organizations with expertise in conflict prevention and peacebuilding. Key panelists will discuss experiences of consultation and collaboration to foster cooperation across these levels.