REN21, the Renewable Energy Policy Network for the 21st Century, is a policy network that provides a forum for international leadership in renewable energy policy, in order to share knowledge and facilitate the rapid growth of renewable energy technologies in developing countries and industrialised economies.

The network was launched in June 2005 as a result of discussion held the previous year at the International Conference for Renewable Energies in Bonn, Germany. Its secretariat operates from offices in Paris, France, and is provided by the United Nations Environment Programme and the Deutsche Gesellschaft für Technische Zusammenarbeit (German Technical Cooperation), in collaboration with the International Energy Agency. Like the Bonn Conference, REN21 distinguishes itself through its flexible nature and multi-stakeholder participation intended to provide a dynamic alternative to the official international fora. Its participants and members are drawn from a wide variety of bodies, including national and local governments, international associations and institutions, NGOs, the private sector, relevant partnerships and scientific panels, and other interested parties.

REN21 has produced a number of internationally recognised reports on renewable energy policy and the development of the renewables marketplace. Since 2005 REN21 has produced an annual Renewables Global Status Report, with Eric Martinot and Janet Sawin as lead authors.