Public broadcasting involves radio, television and other electronic media outlets whose primary mission is public service. In many countries of the world, funding comes from governments, especially via annual fees charged on receivers. In the United States, public broadcasters may receive some funding from both federal and state sources, but generally most of their financial support comes from underwriting by foundations and businesses (ranging from small shops to corporations), along with audience contributions via pledge drives. The great majority operate as private not-for-profit corporations.