Countdown is a British game show involving word and mathematical tasks that began airing in November 1982. It is broadcast on Channel 4 and is most recently presented by Colin Murray, assisted by Rachel Riley with lexicographer Susie Dent. It was the first programme to be broadcast on Channel 4 and 90 series have been broadcast since its debut on 2 November 1982. With over 8,000 episodes, Countdown is one of Britain's longest-running game shows; the original French version, Des chiffres et des lettres (Numbers & Letters), ran on French television almost continuously from 1965 until 2024.

The two contestants in each episode compete in three game types: ten letters rounds, in which they attempt to make the longest word possible from nine randomly chosen letters, four numbers rounds, in which they must use arithmetic to reach a random target figure from six other numbers and the conundrum, a buzzer round in which the contestants compete to solve a nine-letter anagram. During the series heats, the winning contestant returns the next day until they either lose or retire with eight wins as an undefeated "Octochamp". The best eight contestants are invited back for the series finals, which are decided in knockout format. Contestants of exceptional skill have received national media coverage and the programme, as a whole, is widely recognised and parodied within British culture.

Countdown was produced by Yorkshire Television and was recorded at The Leeds Studios for 27 years, before moving to the Manchester-based Granada Studios in 2009. Following the development of MediaCityUK, Countdown moved again in 2013 to the new purpose-built studios at Dock10 in Greater Manchester.