Channel 4 is a British free-to-air public broadcast television channel owned and operated by Channel Four Television Corporation. It is publicly owned but, unlike the BBC, it receives no public funding and is funded entirely by its commercial activities, including advertising. It began its transmission in 1982 and was established to provide a fourth television service in the United Kingdom. At the time, the only other channels were the licence-funded BBC1 and BBC2, and a single commercial broadcasting network, ITV.

Originally a subsidiary of the Independent Broadcasting Authority (IBA), the station is now owned and operated by Channel Four Television Corporation, a public corporation of the Department for Culture, Media and Sport, which was established in 1990 and came into operation in 1993. Until 2010, Channel 4 did not broadcast in Wales, but many of its programmes were re-broadcast there by the Welsh fourth channel S4C. In 2010, Channel 4 extended service into Wales and became a nationwide television channel. The network's headquarters are in London and Leeds, with creative hubs in Manchester, Glasgow and Bristol.

Before Channel 4 and S4C, Britain had three terrestrial television services: BBC1, BBC2, and ITV, with BBC2 the last to launch in 1964. The Broadcasting Act 1980 began the process of adding a fourth channel; Channel Four Television Company was formally created in 1981, along with its Welsh counterpart.

The notion of a second commercial broadcaster in the United Kingdom had been around since the inception of ITV in 1954 and its subsequent launch in 1955; the idea of an "ITV2" was long expected and pushed for. Indeed, television sets sold throughout the 1970s and early 1980s often had a spare tuning button labelled "ITV 2" or "IBA 2". Throughout ITV's history and until Channel 4 finally became a reality, a perennial dialogue existed between the GPO, the government, the ITV companies and other interested parties, concerning the form such an expansion of commercial broadcasting would take. Most likely, politics had the biggest impact leading to a delay of almost three decades before the second commercial channel became a reality.

One benefit of the late arrival of the channel was that its frequency allocations at each transmitter had already been arranged in the early 1960s when the launch of an "ITV2" was anticipated. This led to good coverage across most of the country and few problems of interference with other UK-based transmissions; a stark contrast to the difficulties associated with Channel 5's launch almost 15 years later.

At the time the fourth service was being considered, a movement in Wales lobbied for the creation of dedicated service that would air Welsh language programmes, then only catered for at off-peak times on BBC Wales and HTV. The campaign was taken so seriously by Gwynfor Evans, former president of Plaid Cymru, that he threatened the government with a hunger strike were it not to honour the plans.

The result was that Channel 4 as seen by the rest of the United Kingdom would be replaced in Wales by S4C (Sianel Pedwar Cymru, meaning "Channel Four Wales" in Welsh). Operated by a specially created authority, S4C would air programmes in Welsh made by HTV, the BBC and independent companies. Initially, limited frequency space meant that Channel 4 could not be broadcast alongside S4C, though some Channel 4 programmes would be aired at less popular times on the Welsh variant; this practice continued until the closure of S4C's analogue transmissions in 2010, at which time S4C became a fully Welsh channel. With this conversion of the Wenvoe transmitter group in Wales to digital terrestrial broadcasting on 31 March 2010, Channel 4 became a nationwide television channel for the first time.

Since then, carriage on digital cable, satellite and digital terrestrial has introduced Channel 4 to Welsh homes where it is now universally available.