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Mass media in the United States play a very important role in maintaining a shared national culture and in the formation of public opinion.The media help to standardize cultural patterns by transmitting the same movies and popular music throughout the country，as well as various other content such as news and talk shows.They also influence societal values and affect the nation’s electoral process by disseminating huge amounts of its commercial and political advertisements.Finally，the media function as a“watchdog”over the government as they are free from government control.

Newspapers are the oldest form of mass media.The United States has around 1，700 daily newspapers and over 8，200 weekly newspapers.More than two⁃thirds of American adults read one or another of the nation’s daily newspapers.There is no official national newspaper，although some American newspapers are very influential.The top five newspapers circulation as of 2013 were The Wall Street Journal，The New York Times，USA Today，The Los Angeles Times，and New York’s Daily News.The Washington Post is also very influential because of it’s coverage of national politics and government.Since the 1990s，newspapers have faced severe competition from the Internet for advertising.As a result，hundreds of newspapers have closed and the total number of jobs for newspaper journalists has fallen by about one⁃third since 2005.

Radio became an essential source of entertainment and information during the Great Depression and World WarⅡ.After the war，television replaced radio as the most popular medium for entertainment and news.To adjust，radio began to emphasize music programs which were spiced with news and stories.Radio grew very rapidly in the 1950s when automobile manufacturers began to equip cars with radios as standard accessories.On average，Americans currently listen to radio for about 25 hours a week.

The United States has around 10，000 broadcasting radio stations.The majority of stations are linked nationally through networks and Premier Networks.In addition to commercial stations，the U.S.has over 1，500 public radio stations，most of which are affiliated with the National Public Radio network（NPR）;many of these are run by universities and public authorities for educational purposes.The Voice of America（VOA）presents the viewpoint of the U.S.government to people all over the world.VOA programs are broadcast via shortwave in 47 languages，reaching some 93 million listeners all over the world each week.