<P> In American television terminology, a fourth network is a reference to a fourth broadcast (over-the - air) television network, as opposed to the Big Three television networks that dominated U.S. television from the 1950s to the 1990s: ABC, CBS and NBC . </P> <P> When the U.S. television industry was in its infancy in the 1940s, there were four major full - time television networks that operated across the country: ABC, CBS, NBC and the DuMont Television Network . Never able to find solid financial ground, DuMont ceased broadcasting in August 1956 . Many companies later began to operate television networks which aspired to compete against the Big Three . However, between the 1950s and the 1980s, none of these start - ups endured and some never even launched . After decades of these failed "fourth networks", many television industry insiders believed that creating a viable fourth network was impossible . Television critics also grew jaded, with one critic placing this comparison in the struggles of creating a sustaining competitor to the Big Three, "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 ." </P> <P> The October 1986 launch of the Fox Broadcasting Company was met with ridicule . Despite the industry skepticism and initial network instability (due to its early struggles in launching hit programs), the Fox network eventually proved profitable by the early 1990s, becoming the first successful fourth network and eventually surpassing the Big Three networks in the demographics and overall viewership ratings by the early 2000s . </P> <P> In the 1940s, four television networks began operations by linking local television stations together via AT&T's coaxial cable telephone network . These links allowed stations to share television programs across great distances, and allowed advertisers to air commercial advertisements nationally . Local stations became affiliates of one or more of the four networks, depending on the number of licensed stations within a given media market in this early era of television broadcasting . These four networks--the Columbia Broadcasting System (CBS), the National Broadcasting Company (NBC), the American Broadcasting Company (ABC), and the DuMont Television Network--would be the only full - time television networks during the 1940s and 1950s, as in 1948, the Federal Communications Commission (FCC) suspended approvals for new station construction permits . Although other companies--including Paramount Pictures and the Mutual Broadcasting System--announced network plans or began limited network operations, these companies withdrew from television after the first few years . </P>

By the mid-1980s fox had emerged as a viable fourth network