Energy is vital for a good standard of living, and much of the world's population does not have enough. Affordable and adequate sources of power that do not cause climate change or pollution are crucial; and renewables provide the answer. Wind and solar farms can now provide the cheapest electricity in many parts of the world. Moreover, they could provide all of the world's energy needs. But while market forces are fast helping the transition from fossil fuels to renewables, there are opposing pressures, such as the USA's proposed withdrawal from the Paris Agreement, and the vested interests in fossil fuels. This Very Short Introduction describes the main renewable sources of energy--solar, wind, hydropower, and biomass--as well as the less well-developed ones--geothermal, tidal, and wave. Nick Jelley explains the challenges of integrating renewables into electricity grids, and the need for energy storage and for clean heat; and discusses the opportunities in developing countries for renewable energy to empower millions. He also considers international efforts and policies to support renewables and tackle climate change; and explains recent innovations in wind and solar energy production, battery storage, and in the emerging power-to-gas provision for clean heating.