The early history of television in the United States, particularly between 1956 and 1986, was dominated by the Big Three television networks: the National Broadcasting Company (NBC), the Columbia Broadcasting System (CBS), and the American Broadcasting Company (ABC). The term fourth television network was used within the industry during this era to refer to a theoretical fourth commercial broadcast (over-the-air) television network that would operate as a direct competitor to the "Big Three".
Prior to 1956, the DuMont Television Network operated as an existing fourth network alongside ABC, CBS, and NBC, but an inability to find solid financial ground, a weaker affiliate base, and internal competition from co-owner Paramount Pictures all contributed to DuMont's closure. Multiple companies, film studios and television station owners all either considered, announced or launched networks or program services that aspired to be the "fourth network", but none succeeded. Several of these attempts never advanced from being niche program services, while others either failed to launch or failed after launching. General consensus within the industry and by television critics was that a fourth television network was impossible; one television critic wrote, "Industry talk about a possible full-time, full-service, commercial network structured like the existing big three, ABC, CBS and NBC, pops up much more often than the fictitious town of Brigadoon."[1] Non-commercial educational television, especially with stations aligned with National Educational Television and successor PBS, also found success as program services with network-capable functions.
The launch of Fox in October 1986 was met with ridicule; despite industry skepticism and initial instability, the network eventually proved profitable by the early 1990s, secured rights to NFL football in 1993 and initiated a major affiliate realignment the following year. Fox became the first successful fourth network, eventually surpassing the Big Three networks in demographics and overall ratings by the early 2000s.