Since the aftermath of the 1999 Kosovo Conflict, UNEP has addressed the environmental dimension of insecurities and turned to peacebuilding. This has been risky because it strays close to conflict prevention, identification, or resolution, which lie outside of UNEP’s mandate. I argue that this change in approach results from knowledge creation. UNEP’s experiences about the linkage between environmental degradation and insecurity in postconflict settings motivated its search for opportunities that would legitimize its contribution to postconflict peacebuilding. Seizing on the UN’s Peacebuilding Architecture, UNEP established ECP and, through the program, aimed to develop environmental peacebuilding as a concern through three distinct but interrelated knowledge-building practices: knowledge collection, strategic interpretation, and implementation.