This publication provides an analysis of the 20 year history of the Global Environment Facility (GEF). The aim is to document the ongoing evolution of the GEF and its approaches to biodiversity conservation, development, sustainability, climate change mitigation and adaptation, land degradation, pollution control and other areas of concern, by exploring in detail some of the most salient experiences of the past two decades at the GEF. The publication consists of an analysis of 20 select projects that illustrate the key lessons learned.