In 1983, 50 corporations controlled the vast majority of all news media in the U.S. At the time, Ben Bagdikian was called "alarmist" for pointing this out in his book, The Media Monopoly. In his 4th edition, published in 1992, he wrote "in the U.S., fewer than two dozen of these extraordinary creatures own and operate 90% of the mass media" -- controlling almost all of America's newspapers, magazines, TV and radio stations, books, records, movies, videos, wire services and photo agencies. He predicted then that eventually this number would fall to about half a dozen companies.
This was greeted with skepticism at the time. When the 6th edition of The Media Monopoly was published in 2000, the number had fallen to six. Since then, there have been more mergers and the scope has expanded to include new media like the Internet market. More than 1 in 4 Internet users in the U.S. now log in with AOL Time-Warner, the world's largest media corporation.
In 2004, Bagdikian's revised and expanded book, The New Media Monopoly, shows that only 5 huge corporations -- Time Warner, Disney, Murdoch's News Corporation, Bertelsmann of Germany, and Viacom (formerly CBS) -- now control most of the media industry in the U.S. General Electric's NBC is a close sixth.
--Media Reform Information Center, Links and Resources on Media Reform
(Borrowed from an article on The Existentialist Cowboy's site.)