List of United States over-the-air television networks

In the United States, for most of the history of broadcasting, there were only three or four major commercial national terrestrial networks. From 1946 to 1956, these were ABC, CBS, NBC and DuMont. From 1956 to 1986, the "Big Three" national commercial networks were ABC, CBS, and NBC (with a few limited attempts to challenge them, such as National Telefilm Associates's NTA Film Network, the Overmyer Network, & even DuMont shareholder Paramount Pictures's Paramount Television Network). From 1954 to 1970, National Educational Television was the national clearinghouse for public TV programming; the Public Broadcasting Service (PBS) succeeded it in 1970.
Today, more than fifty national free-to-air networks exist. Other than the non-commercial educational (NCE) PBS, which is composed of member stations, the largest terrestrial television networks are the traditional Big Three television networks (ABC, CBS and NBC). Many other large networks exist, however, notably Fox and The CW which air original programming for two hours each night instead of three like the original "Big Three" do, as well as MyNetworkTV, which feature reruns of recent popular shows with little to no original programming, and Ion Television, which has had the same format since around 2007 but has started to pursue sports properties. Fox has just about the same household reach percentage as the Big Three, and is therefore often considered a peer to ABC, CBS, and NBC since it has also achieved equal or better ratings since the late 1990s; as of 2019, it also programs the equivalent amount of sports programming as the Big Three. Most media outlets now include Fox in what they refer to as the "Big Four" TV networks.
The transition to digital broadcasting in 2009 has allowed for television stations to offer additional programming options through digital subchannels, one or more supplementary programming streams to the station's primary channel that are achieved through multiplexing of a station's signal. A number of new commercial networks airing specialty programming such as movies, reruns of classic series and lifestyle programs have been created from companies like Weigel Broadcasting, Sinclair Broadcast Group and even owners of the major networks such as Fox Corporation (through the Fox Entertainment subsidiary), Paramount Global (through the CBS Media Ventures subsidiary), The Walt Disney Company (through the Walt Disney Television subsidiary) and Comcast (through the NBCUniversal subsidiary). Through the use of multicasting, there have also been a number of new Spanish-language and non-commercial public TV networks that have launched.
Free-to-air networks in the U.S. can be divided into five categories:
Each network sends its signal to many local affiliate television stations across the country. These local stations then air the "network feed", with programs broadcast by each network being viewed by up to tens of millions of households across the country. In the case of the largest networks, the signal is sent to over 200 stations. In the case of the smallest networks, the signal may be sent to just a dozen or fewer stations.
As of the 2016–17 television season, there are an estimated 118.4 million households in the U.S. with at least one TV set.
All of the networks listed below operate a number of terrestrial TV stations. In addition, several of these networks are also aired on pay television services.
Additionally, several of the cable-oriented theme channels (e.g. music or shopping channels) have obtained broadcast clearances, usually on low-power stations, in many markets.
Additionally, Televisa, which distributes programming to Univision in the United States, operates in Mexico, but the company's networks (Canal de las Estrellas, Canal 5 and Nueve) have certain stations which can be received in parts of the U.S. located along and near the Mexican border, and likewise with the American networks have affiliates located or receivable in Mexican border cities. Some Mexican border stations (such as the former English-language ABC/Fox/CW affiliate XETV-TDT in Tijuana) who formerly maintained affiliations with U.S.-based English or Spanish networks, but mainly targeted their programming at their American border city (more than the Mexican metropolitan area that they are based in or merely licensed to).
Although the English-language programming model in the U.S. traditionally relies on the network and its stations handling programming responsibilities, Spanish language networks handle most of the responsibility for programming, while affiliates are limited to breakaways from the network feed to provide local news, public affairs and/or entertainment programming as well as local advertising. As such, all Spanish language networks primarily available on broadcast TV operate national feeds that are distributed to cable and satellite providers in markets without a local affiliate. Spanish-language independent stations also exist, although (particularly with the launch of Estrella TV), these are very limited and they mainly exist in markets with a large Hispanic and Latino American population.
Several religious networks allow their broadcast affiliates to carry their programming out-of-pattern through clearance arrangements, notably TBN, 3ABN, Hope Channel and World Harvest Television.