Big Three television networks

For most of the history of television in the United States, the Big Three dominated, controlling the vast majority of television broadcasting.[5] DuMont ceased regular programming in 1955; the NTA Film Network, unusual in that its programming, all pre-recorded, was distributed by mail instead of through communications wires, signed on in 1956 and lasted until 1961. From 1961, and lasting until the early 1990s, there were only three major networks. Every hit series appearing in the Nielsen top 20 television programs and every successful commercial network telecast of a major feature film was aired by one of the Big Three networks.[6]

There were attempts by other companies, such as the Overmyer Network, to enter the television medium, but all of these ventures lasted only for brief periods. The prohibitive cost of starting a broadcast network, coupled with the difficulty of competing with the massive distribution of the Big Three networks, and the infancy and complexities of UHF broadcasting before cable television became commonplace in the 1980s, led to the downfall of almost all new network ventures; most media markets were limited to no more than three VHF channels, and even after the All-Channel Receiver Act was passed in 1961, the VHF stations were far more efficient and their signals could reach a greater range than their UHF counterparts (see also: UHF television broadcasting § UHF vs VHF). As the Big Three networks had already affiliated with most of the more desirable VHF stations, and the full-service approach of the time meant that the networks programmed almost the entire broadcast day, leaving little room for even off-prime-time programming, that left any upstart network to settle for the inferior UHF outlets. Those networks that could have had the resources to compete, such as Canada's CTV Television Network, which briefly attempted an American expansion via WNYB (channel 26 in Buffalo, New York, now a religious station), were forced off the air through legal threats.

A viable fourth television network in the commercial sense would not again become competitive with the Big Three until Fox was founded in October 1986 from some of the assets and remnants of the DuMont network, which had become Metromedia after DuMont folded, and were acquired by News Corporation earlier in 1986.[7] Fox, which began as a distant fourth network, leapfrogged into major network status in 1994 after must-carry rules took effect; the rules allowed Fox affiliates to force their way onto cable lineups, and the network's affiliation deal with New World Communications, which it later purchased in 1996, and the acquisition of National Football League broadcast rights brought a wave of new Fox affiliates.

Since its founding, Fox has surpassed ABC and NBC in the ratings during the early primetime hours in which it competes against the longer established networks, becoming the second most-watched network behind CBS during the 2000s. During the 2007–08 season, Fox was the highest-rated of the major broadcast networks, as well as the first non-Big Three network to reach first place, but it lost the spot in the 2008–09 season and dropped to a close second. From 2004 to 2012, Fox also dominated U.S. television in the lucrative and viewer-rich 18-49 demographics, in large part due to the success of its NFL coverage and its top rated prime time program, American Idol. Given the network's success in its prime time and sports offerings, it has been occasionally included with the Big Three, in which case the phrase "Big Four" is used.

Although Fox has firmly established itself as the nation's fourth major network with its ratings success, it is not considered part of the Big Three. Among Fox's differences with the Big Three is its reduced weekday programming. It lacks national morning and evening news programs; Fox has a news division consisting of cable and radio operations, but does not provide content for the broadcast television network other than a weekly news analysis program, limited special breaking news reports and an affiliate news service for its stations called Fox News Edge. Fox does not feature any daytime programming, a third hour of primetime, late-night talk shows, and Saturday morning children's programming. Fox had an extensive lineup of children's programs throughout the 1990s called Fox Kids, but sold the division to The Walt Disney Company in 2001 as part of its sale of cable network Fox Family Channel, after which 4Kids Entertainment supplied the network's children's lineup until 2008.

Outside prime time, Fox affiliates either produce their own programming or run syndicated shows. Fox is also the only one of the four major networks to include a regular block of infomercials on its lineup, via the Weekend Marketplace Saturday morning block.

Other networks eventually launched in an attempt to compete with the Big Three as well as Fox, although these "netlets" have been unable to ascend to the same level of success. The WB[8] and UPN launched in 1995; like Fox, they both added nights of prime time programming over the course of a few years, although The WB was the only one that aired any on weekends, carrying a Sunday night lineup for all but its first half-season on the air.

Both networks mainly aired only prime time and children's programming. The latter was the only form of weekday daytime programming offered by either one, although UPN discontinued its children's lineup in 2003 at the conclusion of a content deal with Disney, and UPN aired sports programming via the short-lived XFL, as well as WWF SmackDown!.

While The WB and UPN each had a handful of popular series during their existences, they struggled for overall viewership and financial losses. This led their respective parent companies, Time Warner and CBS Corporation, to shut them down in 2006 to jointly launch The CW,[9] which initially featured a mix of programs from both predecessors, as well as some newer shows after the launch.

Fox launched MyNetworkTV at the same time as The CW, with a lineup of English language telenovelas;[10] it later shifted toward unscripted programs and movies, though its persistent lack of ratings success led News Corporation to convert it into a programming service, relying on a lineup of acquired series, in 2009.[11]

Likewise, the Public Broadcasting Service (PBS), which has existed since 1970, is not considered part of the "big three" networks. PBS operates as a noncommercial service with a much different distribution model compared to the major networks; its member stations in essence own the network rather than the traditional mode of a network owning some of its stations and affiliating with additional stations owned by other broadcasters, and it maintains memberships with more than one educational station in a few markets.

Today, the "Big Three" control only a relatively small portion of the broadcasting market in the United States; by 2005, its share was estimated at a combined 32%.[1] The Big Three's market share has dwindled considerably as a result of growing competition from other broadcast networks such as Fox, The CW, and MyNetworkTV, and more recently Spanish language networks such as Univision and Telemundo, as well as national cable and satellite channels such as TNT, ESPN, and AMC, and web channels such as Netflix.[1]