The United States has a decentralized, market-oriented television system. Unlike many other countries, the United States has no national broadcast programming services. Instead, local media markets have their own television stations, which may be affiliated or owned and operated by a TV network. Stations may sign affiliation agreements with one of the national networks. Except in very small markets with few stations, affiliation agreements are usually exclusive: If a station is an NBC affiliate, the station would not air programs from ABC, CBS or other networks.

However, to ensure local presences in television broadcasting, federal law restricts the amount of network programming local stations can run. Until the 1970s and '80s, local stations supplemented network programming with a good deal of their own produced shows. Today, however, many stations produce only local news shows. They fill the rest of their schedule with syndicated shows, or material produced independently and sold to individual stations in each local market.

The three major commercial television networks in the U.S. include NBC and CBS, which date to the early days of television (in fact, they both began in the 1920s as radio networks), and ABC, founded, also as a radio network, in 1943. In big cities, affiliates of these networks almost always broadcast in the VHF band, which, in the days before cable became widespread, was premium real estate.

Major-network affiliates run very similar schedules. Typically, they begin weekdays with an early-morning locally produced news show, followed by a network morning show, such as NBC's Today, which mixes news, weather, interviews and music. Syndicated programming, especially talk shows, fill the late morning, followed often by local news at noon (Eastern Time). Soap operas dominate the early afternoon, while syndicated talk shows such as The Oprah Winfrey Show appear in the late afternoon. Local news comes on again in the early evening, followed by the national network's news program at 6:30 or 5:30 p.m., followed, in the Central Time zone, by more news.

More syndication occupies the next hour (or ½ hour in the Central time zone, called prime access slot) before the networks take over for prime time, the most-watched three hours of television. Typically, family-oriented comedy programs led in the early part of prime time, although in recent years, reality television like Dancing with the Stars has largely replaced them. Later in the evening, dramas like CSI: Crime Scene Investigation and Grey's Anatomy air.

At 10 or 11 p.m., another local news program comes on, usually followed by late-night interview shows, such as Late Show with David Letterman. Rather than sign off for the early hours of the morning (as was standard practice until the 1980s or so), TV stations now fill the time with syndicated programming or 30-minute advertisements, known as infomercials.

Saturday mornings usually feature network programming aimed at children (including animated cartoons), while Sunday mornings include public-affairs programs that help fulfill stations' legal obligations to provide public-service programming. Sports and infomercials can be found on weekend afternoons, followed again by the same type of prime-time shows aired during the week.

Until 1987, all English-language stations not affiliated with the big three networks were independent, airing only locally produced and syndicated programming. Many independent stations still exist in the U.S., usually broadcasting on the UHF band. Syndicated shows, often reruns of old TV series and old movies, take up much of their schedule.

In 1986, however, the Fox Broadcasting Company launched a challenge to the big three networks. Thanks largely to the success of shows like The Simpsons, as well as the network's acquisition of rights to show National Football League games, Fox has established itself as a major player in broadcast television. However, Fox differs from the three older networks in that it does not air a nightly news program, its prime-time schedule is only two hours long, and some of its big-city affiliates still broadcast on UHF. Its only scheduled news program is FOX News Sunday, on Sunday mornings; FOX prefers to use the cable FOX News Channel for its news programming, giving affiliates more time to carry local news. Most FOX affiliates now have local newscasts, usually airing an hour earlier competing with network dramas, rather than other local newscasts.

In the 1990s, three new networks -- The WB, UPN and PAX -- joined the scene. The fledging WB and UPN merged into The CW in fall 2006, while News Corp's MyNetworkTV, created to replace UPN programming on FOX's O&Os, debuted in fall 2006 as well. PAX, now known as "ION Television," has had very low ratings since its launch and is no longer considered a competitor to the larger over-the-air networks.

ION broadcasts 24 hours a day, 7 days a week, making the ION network totally responsible for its affiliates. MyNetworkTV broadcasts 12 hours a week, Monday through Saturday. The CW broadcasts 13 hours a week in prime time, 10 hours in daytime.

Univision, a network of Spanish language stations, is the fifth-largest TV network behind NBC, CBS, ABC and Fox. Its major competition is Telemundo, a sister network of NBC. Univision-owned TeleFutura, aimed at a younger Hispanic demographic, and Azteca America, the American version of Mexico's TV Azteca, are two other popular Spanish-language over-the-air networks.

In addition, the Miami-based Haitian Television Network offers locally produced Haitian Creole and French language programming in Miami and parts of New Jersey, New York City, and Boston.

Public television has a far smaller role than in most other countries. There is no state-owned broadcasting authority. Instead, the federal government subsidizes non-commercial television stations through the Corporation for Public Broadcasting. The income received from the government is insufficient to cover expenses and stations rely on corporate sponsorships and viewer contributions.

American public television stations air programming that commercial stations do not offer, such as educational, including cultural, and public affairs programming. Most public TV stations are affiliates of the Public Broadcasting Service, sharing programs like Sesame Street and Masterpiece Theatre. Unlike the commercial networks, PBS does not produce its own programming; instead, individual PBS stations create programming and provide these to other affiliates. New York City's municipally-owned broadcast service, NYCTV, creates original programming that airs in several markets. Few cities have major municipally-owned stations.

Many religious broadcasting stations exist, also surviving on viewer contributions.

Until the 1970s, cable television was used only to rebroadcast over-the-air TV to areas that had trouble receiving signals. But in that decade, national networks dedicated exclusively to cable broadcasting appeared, along with cable-TV systems that provided service to major cities. Today, most American households receive cable TV, and cable networks collectively have greater viewership than broadcast networks.

Unlike broadcast networks, most cable networks air the same programming nationwide. Top cable networks include USA network, ESPN (sports), MTV (music), CNN (news), Sci Fi (science fiction), Disney Channel (family), Nick (Children's), Discovery Channel (documentaries), TBS (comedy), TNT (drama) and Lifetime (women's)

Cable-TV subscribers receive these channels through local cable system operators, who receive the programming from the networks and transmit them into homes. Usually, local governments award a monopoly to a system operator to provide cable-TV service in a given area. By law, cable systems must include local over-the-air stations in their offerings to customers.

Today Direct broadcast satellite television services, which became available in the U.S. in the 1990s, offers programming similar to cable TV. Dish Network and News Corporation's DirecTV are the major DBS providers in the country. Satellites were originally launched and used by the Television networks as a method of distributing their programs from headquarters to local affiliates. In the 1970s individuals in remote locations, without access to Terrestrial television broadcasts, found they could get free television by installing large satellite dishes and aiming them at the various satellites owned by the networks. This had the additional benefit of providing channels that others could not receive. This included programs without commercials, live feeds not intended for broadcast, broadcasts from other countries and eventually cable television programming. To prevent people from receiving pay content for free, satellite transmissions are now scrambled. Newer transmission technology enabled satellite dishes to be much smaller and subscription services were developed.