Economic growth, social inclusion, and environmental protection must go hand in hand to achieve the Sustainable Development Goals (SDGs). As a central actor in the United Nations Development System, the United Nations Development Program (UNDP) supports sustainable development practices that help countries grow in ways that adapt to the challenges posed by climate change and that preserve life on land and below water. UNDP has been a major implementing partner of the Global Environment Facility (GEF) since its establishment in 1991, addressing our planet’s most pressing environmental problems. Over time, 74 million people in 137 countries worldwide directly benefited from this shared portfolio.1 to inform future initiatives, UNDP’s Independent Evaluation Office (IEO) has undertaken a review of lessons from past evaluations of UNDP-supported environment initiatives financed through the GEF. The purpose is to provide evidence-based advice to UNDP country offices on ‘what works (or doesn’t) and ‘how’ regarding the design and implementation of such a program. This paper focuses on lessons in the areas of climate change mitigation and adaptation, land degradation, conservation, and sustainable use of biodiversity and international waters.