This chapter examines the United Nations Environment Programme’s (UNEP) pivotal role in fostering peaceful change within global environmental governance over fifty years. UNEP’s inception at the Stockholm Conference, informed by scientific consensus and diplomatic foresight, marked a transformative approach to international collaboration for sustainability. This analysis employs a tridimensional framework – practical, political, and personal – to interrogate UNEP’s impact on environmental governance. It delves into the vision for UNEP at its foundational moment, its operational evolution, and its adaptive strategies in navigating the complex interplay of global power dynamics, from large powers to small states. The chapter highlights UNEP’s leadership in key environmental achievements, notably the reversal of ozone layer depletion and its emergent role in conflict resolution and peacebuilding. By focusing on UNEP’s trajectory and contributions, this narrative underscores the intricate ties between environmental protection and peace. The overarching theme emphasizes the necessity of continuous political mobilization and scientific engagement to address the urgent environmental crises of our time, echoing UNEP’s call for renewed, cooperative, and ecologically conscious global governance.