Over the past decade, technologies for variable renewable energy (VRE) sources such as wind and solar have undergone dramatic cost reductions in many markets. For many countries, the possibility of achieving high levels of VRE penetration is now within sight. Over 144 countries have set ambitious renewable energy targets, and more than 100 have already enacted policies or measures to promote the use of renewables. However, the prospect of meeting a sizeable share of electricity demand through VRE sources also requires significant expansion and modernization of existing electrical grids. Integration of VRE into electricity systems has become a prominent issue and research focus for utilities, private companies, and international organizations. ESMAP helps countries to solve immediate VRE challenges and provides long-term support to transform power systems planning, operations and regulatory frameworks.