The thinking man's game show, and the face of Channel 4 in Britain, having been the first programme aired on the channel in 1982 and running ever since. Two contestants face off in a series of Letters and Numbers Rounds, each hoping to score more points than the other. Every round is timed to 30 seconds, with a big clock ticking down behind the contestants. It was a companion to Fifteen to One until that show's demise. It was paired with Deal or No Deal for a whole decade, but following that show's demise, Countdown's companion is now a revived Fifteen to One.

Countdown is based on a French game much more straightforwardly titled The Numbers and Letters (Des chiffres et des lettres). There is also an Australian version titled Letters and Numbers, (a more direct reference to the French title) to avoid confusion with the Australian program titled Countdown, a music video show (see below) and pay homage to the original French version.

In January 2012, the stars of the panel comedy show 8 Out of 10 Cats did an Affectionate Parody of Countdown for the Channel 4 Mashup event, which mixed one show with another for one night of hilarity. It was titled — wait for it — 8 Out of 10 Cats Does Countdown. It proved so popular that it eventually became a series in its own right (and in fact has more or less replaced the original 8 Out of 10 Cats completely), premiering in July 2013. This version is played with two teams of two, with Jon Richardson, Sean Lock (From Series 1 until his death in 2021) and Rob Beckett (From Series 29 onwards) being the resident captains. Following Sean's death, he would be replaced by guest captains until Series 29, where Rob Beckett, one of the recurring members, would become the permanent team captain.

The rounds are as follows, with the first two repeated several times:

• Letters Round: Nine random letters are drawn, one at a time, with the player requesting either a vowel or consonant on each draw. Once all the letters are on the board, the players try to form the longest single word they can. Only the longer valid word scores: one point per letter, or 18 for using all nine. Currently played 10 times per episode.
• Numbers Round: The player requests anywhere from zero to four "large numbers" (25, 50, 75, or 100) chosen at random, and enough "small numbers" (two each of 1 through 10) are drawn to give six altogether. A random three-digit number is generated, and the players must use the four basic maths operations (addition, subtraction, multiplication, and division) to get as close to it as they can. No fractions, decimals or non-positive numbers are allowed. Only the player closer to the number scores, provided their calculations are correct: 10 points for hitting it exactly, 7 for being 1-5 away, 5 for being 6-10 away. Currently played four times per episode.
• Conundrum: Always played as the final round of each episode. The players are shown a group of short words totaling nine letters, and the first to buzz in and rearrange the letters into a single word scores 10 points. If the scores are tied after this round, additional Conundrums are played until the tie is broken. When the scores differ by 10 points or less going into this round, it is called a "Crucial Countdown Conundrum."
• A Teatime Teaser is played for the home audience at each commercial break, in which a set of short words is displayed, and the host reads a cryptic clue to a single word that can be anagrammed from them. The solution is given at the start of the next segment. (e.g. SADMOODY with a clue of "We'll all be sad and moody when this arrives" leads to DOOMSDAY.) The Cats version has Conundrums and Teasers with rude words/innuendos but mostly innocent answers (e.g. ISEEPORN - "Who came first?" leads to PIONEERS.)

No relation to the 1968 Robert Altman film, the Australian music show^note The Australian version of the game show is called Letters and Numbers, the American political news/commentary show/podcast Countdown with Keith Olbermann, or the weekly comic series that was later re-titled Countdown to Final Crisis.

This show provides examples of:

• Alliterative Name:
  • The Countdown Conundrum. It becomes a "Crucial Countdown Conundrum" if the players' scores differ by 10 or less.
  • The Teatime Teaser that bridges each commercial break.
  • Rachel Riley.
• And Your Reward Is Clothes:
  • Or, as befits the game, books: the grand prize is a dictionary. Not just any dictionary, though, but the full 23-volume leather-bound complete Oxford English Dictionary. It's so huge, it actually causes problems for some winners because it takes up so much space.
  • The winner of series 31, David Acton, refused to accept the leather-bound dictionary because of his strict veganism. He chose to receive the dictionary on CD instead, giving the significant difference in value to charity.
  • Every newly crowned champion receives a teapot shaped like the show's 30-second time clock. Defeated contestants and retiring undefeated champs receive an assortment of Countdown-themed merchandise as a Consolation Prize.
• Artificial Stupidity: The computer which generates the target numbers during the Numbers Round has a habit of throwing out ludicrously easy ones from time to time, usually requiring only two or three of the six numbers on the board. Here's an example. Contestants sometimes try to be clever in these situations, but most of the time this trick backfires and gives the opponent a chance at some easy points.
• Ascended Extra: Susie Dent first appeared in 1992 as one of the show's many rotating lexicographers whose job was simply to adjudicate on a submitted word's validity, however she proved popular with viewers and as time passed the other lexicographers were gradually phased out. She now has her own section of the show where she explains the meanings behind various commonly-used words and phrases, is credited as a co-host alongside Rachel Riley and has appeared in more episodes than any other person. Possibly a somewhat Downplayed example, as she was chosen as the letters and numbers assistant in the 1997 Christmas special and was also the lexicographer in the "Gotcha" episode for Noel's House Party (which required a lot of planning). This suggested that she was perhaps already seen as a cut above the other lexicographers on the show.
• Audience Participation: Until 2020, if neither player can solve the Conundrum, the host asked if anyone in the audience had the answer and picked someone to call it out (with the correct guesser being awarded a Countdown mug). Done away with once the show resumed filming after production shutdowns caused by the COVID-19 Pandemic and got rid of its studio audience.
• Blinking Lights of Victory: An earlier iteration of the set would flash when one of the contestants gets a nine-letter word.
• Blonde, Brunette, Redhead: In play between June 2021 and July 2022, when Anne Robinson was the host, giving the show the combination of blonde (Rachel), brunette (Susie) and redhead (Anne).
• Bonus Round: Occasionally seen on 8 Out of 10 Cats Does Countdown, played for extra points. So far, bonus rounds have included a pub quiz, penalty shootout, drawing a life model, and "Carrot In A Box" (a bluffing game carried over from the parent show).
• Bonus Space: A variant. Any valid nine-letter word in the Letters Round scores 18 points.
• Brainy Brunette: Carol Vorderman. Also Susie Dent in Dictionary Corner.
• Catchphrase: Several, used by the various hosts to start the clock: "Stand by," "Clock time," "And here's the countdown clock," "And your time starts... now," and sometimes just "Countdown." Colin Murray favors "Numbers up" for the numbers rounds, "Last numbers" for the fourth and final one on a Friday, and "We'll be back tomorrow - you can count on us!" to close the show.
• Consolation Prize: Losing players and retiring undefeated champions take home a collection of show-branded merchandise.
• Crossover:
  • Being as iconic as it is, the game has appeared in other shows as part of some kind of task — notably to embarrass Ant and Dec on Saturday Night Takeaway, and as a shopping budget task on Big Brother.
  • A more straightforward crossover happened with 8 Out of 10 Cats as part of Channel 4's "mash-up" night in 2012. The format proved so popular that it has developed into a series in its own right.
• Cute Kittens: On Catsdown, Jimmy actually brings eight kittens in during one round to distract the contestants. It works, but he also spends the round literally herding cats when they escape from their baskets.
• Didn't Think This Through: The above-mentioned "kitten incident" in one episode of the 8 Out of 10 Cats crossover, lampshaded when they point out that Jimmy didn't think it through.
• Dumb Blonde: Completely averted with Rachel Riley, who replaced Carol Vorderman as the co-host as of 2009. She studied mathematics at Oxford and can usually work out an exact solution for the numbers round if neither of the contestants can get it. On the rare occasions that she can't figure one out on the spot, she works on it either during a commercial break or at home.
• Early-Installment Weirdness:
  • Prior to Des Chiffres et des Lettres in France, the words rounds were a separate show called Le mot les plus long, in which unused letters were carried on to a next round.
  • The basic format hasn't changed that much since the show started on Channel 4, but there have been some peripheral changes which make watching anniversary repeats a bit strange. For example the existence of several female assistants instead of one (who essentially acts as co-presenter now), the extending of the show from half an hour to three quarters, no Susie Dent as resident lexicographer with her own "origins of words" featurette, no "Teatime Teaser" book-ending the commercial breaks, and (in the first episode) the fact that things did seem a lot more awkward.
    • A few minor-but-noticeable differences in the early episodes include Richard Whiteley commenting on the numbers via voiceover as they appeared on the board, the font of the letters on the board being different (and more difficult to read, at least for the television viewer) and the Conundrum answer being revealed by an assistant instead of it appearing automatically.
  • Before Channel 4 there was also an earlier incarnation, Calendar Countdown which was shown only on Yorkshire Television as an offshoot of regional news programme Calendar. If the pilot (kicking around YouTube somewhere) is anything to go by, the format was a lot different, with rounds not making it into the more famous Channel 4 incarnation and the clock ran for 45 seconds.
• End of an Age: On Carol Vorderman's last show (12 December 2008), the final conundrum was ERACLOSES.^AnswerCASSEROLE
• Fun with Acronyms: CECIL is the Countdown Electronic Computer In Leeds. (Unfortunately, it is now somewhat of a Non-Indicative Name, given how the program has since moved from what used to be YTV, to the ex-Granada studio block in Manchester, and most recently to the new MediaCityUK complex across the river in Salford.)
• Game Show Host: Richard Whiteley is the most well-known.^note He was also a presenter on Yorkshire Television's regional news programme Calendar, earning him the nickname "Twice Nightly Whiteley". He was replaced after his passing in 2005 by Des Lynam, who turned the desk over to Des O'Connor in 2007. Jeff Stelling was the next host, starting in 2009; he left at the end of 2011 and was replaced with Nick Hewer (yes, that Nick Hewer) at the start of 2012. Anne Robinson, host of The Weakest Link (and a Dictionary Corner guest in 1987), succeeded Hewer after he left in June 2021, she was succeeded in July 2022 by Colin Murray, who had previously filled in for Hewer in 2020/21 when the latter was shielding from COVID-19 and until he was vaccinated.^note Murray himself would have to be covered - firstly by Les Dennis and then Jenny Eclair - after testing positive for COVID. Jimmy Carr naturally hosts the panel show spin-off 8 Out of 10 Cats Does Countdown.
• Golden Snitch: Invoked in one of the 8 Out of 10 Cats Does Countdown editions, where the team of Bob Mortimer and Lee Mack (trailing 54-0) seemingly arbitrarily persuade host Jimmy Carr (with some help from Joe Wilkinson) to make the final conundrum worth 100 points. They still manage to lose the conundrum anyway. Similarly, just because Jon Richardson wanted to finish a show with the most points of any Countdown player ever, Jimmy made the conundrum of one episode worth over 800 points (the difference between his lifetime total and that of the all-time leader).
• Heh Heh, You Said "X": On occasion, people have laughed when contestants declared funny or vulgar words, but even the board sometimes gets in on this.^note Poof is a British slang for a homosexual - already everyone was laughing because "Poo" is another word for "Feces" in Britain
• Hidden Depths: One episode had the contestants write poems for a guest appearance by John Cooper Clarke. Johnny Vegas' poem got a standing ovation from most of the panel, including Clarke himself.
• Home Game: Several, including a DVD version.
• Hotter and Sexier: The 8 Out of 10 Cats version naturally features much more ribald humour and uncensored profanity.
• Impossible Pickle Jar: During one of the countdowns in 8 Out of 10 Cats Does Countdown, Jimmy pulled out an enormous jar of pickles from under the desk and attempted to open it, using an assortment of increasingly unlikely tools. In the dying seconds, Rachel walked over and opened it for him, causing him to comment "I loosened that".
• Lovely Assistant:
  • Carol Vorderman up to 2008, Rachel Riley since 2009.^note Carol's initial role was just that of checking the working out in the numbers round and providing a solution if the contestants couldn't, carrying the humorous (if slightly sexist sounding) job title "vital statistician"! (She also shared this role with Linda Barrett in the first two series.) Other hostesses were involved in dealing with the letters and numbers tiles. (They included, at various times: Cathy Hytner, Beverley Isherwood, Karen Loughlin and Lucy Summers) In some seasons of 8 Out Of 10 Cats Does Countdown, Rachel got her own Lovely Assistant in the shape of Joe Wilkinson.
  • "Fabio" and his cohorts are a male example; their collective job is to bring the prizes in and out while wearing very little clothing, and then smile and wave to the audience.
• Luck-Based Mission: Even with the Scrabble-like distribution of letters, forming long words can be tricky. Likewise, not all Numbers Rounds have an exact solution.
• Letters 2 Numbers: The logo used on the French version from 1998-2005 wrote the name as De5 Ch1ffres et de5 Lettres , with some of the e's resembling mirrored 3's.
• Ms. Fanservice: Carol and Rachel.
• Nice Guy: Most of the hosts have been warm and friendly, perhaps above all Richard and Colin. Averted, kind of, with Des Lynam and Anne. Neither were exactly unpleasant, but they were seen as lacking the enthusiasm of most of the other hosts. It is perhaps not surprising that they had the two shortest stints of any Countdown hosts.
• Non Sequitur: In many Letters rounds (rarely Numbers) on the 8 Out of 10 Cats edition, whilst the clock is ticking, Jimmy would take part in a humourous activity, such as blowing up balloons (and then getting lifted up with them), drinking a potion to grow hair quickly or enticing a bird of prey to fly onto his arm. Rachel and occasionally Susie sometimes take part in these segments.
• Number of the Beast: Occasionally 666 will come up as the target sum in the numbers round. This has been shown to disturb members of the audience, as well as some of the players. On one occasion in which the number came up on a Christmas special of the Cats version, Jimmy quipped "Merry Christmas, Satan!" before starting the clock.
• Pungeon Master: Richard Whiteley.
• Running Gag: On the 8 Out of 10 Cats edition, Nick Helm's frighteningly aggressive crush on Susie Dent.
• Ship Tease: Considering how much Richard and Carol seemed to get along on-air, this isn't surprising. To a lesser extent, Des O' and Carol.
• Shout-Out: Some Conundrums and Teasers feature these to some of the panellists. Examples include:
  • The normal version: DESLHINAM, RINGSUSIE, DENTSCENE.^AnswersMISHANDLE, REISSUING, SENTENCED
  • The Cats version: SITONSEAN, RIDEVEGAS, DENTPOOPS.^AnswersSENSATION, GRAVESIDE, POSTPONED
• Significant Anagram: Words score one point per letter in the Letters Round, or 18 points for using all nine, and the Conundrum (always a nine-letter anagram) is worth 10.
• Studio Audience: Used to have one until 2020, when the COVID-19 Pandemic forced it to begin filming without one when it returned. It was later announced that this change would become permanent.
• Sudden Death: If the two players are within 10 points of each other for the final Conundrum, it becomes a Crucial Countdown Conundrum, and the lights dim to emphasize the Serious Business of it all.
• Take That!: When Preston North End got relegated from the Championship, a producer who was a Blackpool fan assembled the Conundrum "PNECRISIS".
• Think Music:
  • About as iconic in the UK as the Jeopardy! theme "Think!" is in America, to the point that people who never even watch the show will start humming it as a hint that you need to hurry up and make a decision). Have a listen.
  • Jon Richardson came up with a new catchy national anthem for Britain using the clock music.
  • The Cats version occasionally features "Tension Rounds" with a techno version of the music (with a voice counting down from 10 seconds), along with pyrotechnics and other stuff blowing up during the round and double points being awarded.
• Timed Mission: All rounds last 30 seconds.
• Unintentionally Unwinnable: The numbers round sometimes generates a target that is impossible to reach with the six chosen numbers. It's still played out under the normal rules and scoring.