SunDay is one day each year for Europe to discover the potential of renewable energy and to celebrate the power of the sun. All events are organised locally, coordinated nationally via National Liaison Officers, and publicized across Europe.

The SunDay initiative of ISES-Europe, the European Unit of the International Solar Energy Society, is supported by networks of nongovernmental associations, including INFORSE, as well as by trade associations, the European Union, and governmental networks.