Public broadcasting may be nationally or locally operated, depending on the country and the station. In some countries a single organization runs public broadcasting. Other countries have multiple public-broadcasting organizations operating regionally or in different languages. Historically, public broadcasting was once the dominant or only form of broadcasting in many countries (with the notable exception of the United States). Commercial broadcasting now also exists in most of these countries; the number of countries with only public broadcasting declined substantially during the latter part of the 20th century.