In Europe, a full transition to 100% renewable energy across all sectors--power, heat, transport and desalination is feasible. Existing renewable energy potential and technologies, including storage, can generate sufficient and secure energy supply at every hour throughout the year. The sustainable energy system would be more cost effective than the existing system, which is primarily based on fossil fuels and nuclear energy. The energy transition is not a question of technical feasibility or economic viability, but one of political will.