A RadioDrama on [[Creator/TheBBC BBC Radio 4]] which later became the basis for [[Franchise/TheHitchhikersGuideToTheGalaxy various spin-offs]]. It (technically) ran for twenty-six years and as many episodes.

It started with only two series (or "Phases") in 1978-1980. It was later mixed-and-matched into the first two novels. It was later revived in 2003 and spawned three more Phases based on the last three books by Creator/DouglasAdams. Another revival in 2018, the Hexagonal Phase, adapted Creator/EoinColfer's entry in the series, ''Literature/AndAnotherThing''.

The cast was fairly consistent across the board, with only Peter Jones and Richard Vernon being replaced between the second and third series due to their deaths in the interim. Even death didn't stop Creator/DouglasAdams from putting in an appearance in the Tertiary and Quintessential Phases, despite the fact that he ''wasn't'' reprising a previous character.

!!The original two seasons contain examples of:
* AndroidsArePeopleToo: Marvin the Paranoid Android was a prototype for robots fitted with Genuine People Personalities. He's never forgiven the Marketing Division of the Sirius Cybernetics Corporation (who defines a robot as "Your plastic pal who's fun to be with") for it.
* ChekhovsGun: Arthur mentions in Fit The Fifth he has a travel Scrabble game on him. [[spoiler: He and Ford use this to find out the question hidden in his brain waves in the next fit.]]
* DeadlyEuphemism: Played with.
** Slartibartfast threatens Arthur that, unless Arthur comes with him promptly, he will be late -- as in "the late [[TheNameIsBondJamesBond Dent Arthur Dent]]".
--->"[[DontExplainTheJoke It's a sort of threat, you see...]]"
** Hig Hurtenflurst explains his use of "revoked" to Arthur by spelling it out as "k-i-l-l-e-d". A subsequent episode reveals that this is part of a larger legal wrangle where (for various reasons) the representatives of a cloning agency were trying to get murder redefined in law. They'd managed to have the word legally changed, but not the spelling.
* FaceDeathWithDignity: As Zaphod, Trillian and Marvin are being eaten by the ravenous Bug Blatter Beast Of Traal:
-->'''Trillian:''' Aaarrgghh, it's got us! If I ever survive this, I'll get a job as Moby Dick's dentist!\\
'''Zaphod:''' Can it Trillian, I'm trying to die with dignity.\\
'''Marvin:''' I'm just trying to die.
* FantasticRacism: The shape-shifting Haggunenons hate all the "filthy rotten samelings".
* {{Foreshadowing}}: Ford mentions in Fit The Fifth that drunk-time traveling earns getting dumped on a prehistoric planet and being told to a evolve into a more responsible life form. [[spoiler: Fit The Sixth ends with him and Arthur stuck on a prehistoric Earth.]]
* GambitRoulette: In this version, Frankie and Benjy Mouse planned Arthur and Trillian's escape from Earth ahead of time as a back-up plan. This would involve them knowing about the Vogons' demolition plans, Ford's presence on Earth and his willingness to save Arthur, and Zaphod teleporting into a particular party and successfully wooing Trillian into leaving Arthur and going following him to the Heart of Gold.
* GiantFlyer: The Brontitall. [[spoiler:Of the Deus Ex Machina Airlines variety. Not really ''that much'' of a spoiler.]]
* GodIsInept: At the very start, we are told that the Guide is more controversial than Oolon Colluphid's philosophical trilogy "Where God Went Wrong," "Some More Of God's Greatest Mistakes," and "Who Is This God Person, Anyway?" Colluphid would go on to write "Well, That About Wraps It Up For God" after He disappears upon learning that the Babel Fish's existence cancelled Him out.
* IdiosyncraticEpisodeNaming: Fit the First, Fit the Second, etc. This is a reference to Creator/LewisCarroll's ''Literature/TheHuntingOfTheSnark''.
* INeedAFreakingDrink: When it's established that (due to the effects of the Infinite Improbability Drive) Ford and Trillian are the only two members of the core cast who haven't coincidentally met before:
-->'''Zaphod''': Oh, god. ''[rapidly]'' Ford, this is Trillian, Hi. Trillian, this is my semi-cousin Ford who shares three of the same mothers as me. Hi. ''[...]'' Zaphod Beeblebrox, this is a very large drink. ''Hi.''
* InUniverseNickname: Marvin is first dubbed "The Paranoid Android" in Fit the Third, where the Heart Of Gold lands on Magrathea.
* ItsALongStory: Lintilla says this when asked by Hurtenflirst why there are duplicates of her running around. When asked for a quick précis, she crams it all down to "Because."
* LargeHam:
** Zaphod, played by Mark Wing-Davey, was written as such [[{{Typecasting}} specifically because he was played by Mark Wing-Davey.]]
** Also Mark Smith, who just happens to chew the scenery as Hig Hurtenflirst!
* MessageInABottle: Arthur and Ford are stranded on prehistoric Earth, and attempt to attract the attention of a passing spaceship by waving a towel at it. A volcano then erupts, covering the towel with lava. [[StableTimeLoop When the Earth is blown up six million years later, the now-fossilized towel gets launched into space and found by Zaphod Beeblebrox in the spaceship Heart Of Gold, who travels back in time and rescues them.]] (Things like this tend to happen whenever you use the Heart Of Gold's "Infinite Improbability" drive.)
* {{Motormouth}}: A space-freighter co-pilot flying to the Guide production-office's homeworld goes on a long-winded rant about what a bunch of sell-outs the Guide management is. The pilot's reply: "...Talk a lot, don't you?" Which provokes ''another'' long rant about how there's nothing to do on this kind of long super-automated trip ''but'' talk.
* MovingBuildings:
** In the scene where Arthur and Ford are first exposed to the Infinite Improbability Drive, they briefly see an apparition of the holiday resort of Southend-on-Sea, Essex, where the sea remains steady as a rock but all the buildings on the seafront roll up and down, like waves.
** The [=h2g2=] building in which Zaphod and Marvin have taken refuge is bodily uplifted by the dread Frogstar Fighters and transported through space to the world of the Infinite Perspective Vortex.
* NoodleIncident: The narrator/Guide mentions in passing that Arthur's only brother was somehow nibbled to death by an [[SeldomSeenSpecies Okapi]].
* PuffOfLogic: God vanishes like this, thanks to the Babel Fish's creation.
-->"I refuse to prove I exist," says God, "for proof denies faith and without faith I am nothing."\\
"But," says Man, "The Babel Fish is a dead giveaway, isn't it. It proves you exist. Therefore, you don't. Q.E.D."\\
"Oh dear," says God, "I hadn't thought of that," and promptly vanishes in a puff of logic.
* PutOnABus: Trillian for the Secondary Phase is in an ArrangedMarriage in some distant part of the galaxy.
* RelaxOVision: During the approach to Magrathea where, supposedly in order to help combat rising stress levels in the galaxy, it was carefully explained to the audience that no one was going to get killed in the ensuing confusion -- although one unidentified person would be bruised on the arm. [[spoiler:It's Arthur.]]
* {{Retronym}}: It wasn't until the radio series were released on tape that the seasons began being referred to as Phases. (This only applies to the first two seasons, the rest were labeled Phases right out of the gate.)
* RippleEffectIndicator: While trapped on prehistoric Earth, Ford and Arthur encounter a hovering spacecraft that keeps appearing and disappearing as they discuss how to react to its presence. They eventually figure out that it has traveled back in time, and that whatever they do next will determine whether the future will be one in which the spacecraft exists and makes the journey; as long as they can see it, they're on the right track, but if it disappears, that's a sign that whatever they're planning to do will result in a future where the spacecraft never visited them in the past.
* SecondEpisodeIntroduction: Zaphod, Trillian, and Marvin.
* ShapedLikeItself: Zaphod and Ford find themselves in a cave made out of marble, very slippery marble. Zaphod tries to compare it to the slipperiest thing Ford can think of. Unfortunately, the slipperiest thing Ford can think of is the marble, leading to the statement "This marble is as slippery as this marble."
* SignificantDoubleCasting: Bill Wallis plays both Prosser (the man in charge of demolishing Arthur's house) and Jeltz (the alien in charge of demolishing Arthur's planet).
* TakeThat: Shooty and Bang Bang, the two trigger-happy but sensitive cops who go after our heroes on Magrathea, are a cruel parody of Series/StarskyAndHutch.
* TrickedIntoSigning:
** The Frogstar Prisoner Relations Officer pretends he wants Zaphod's autograph to trick Zaphod into signing a release form agreeing to be shoved into the Total Perspective Vortex.
** A cloning machine accident results in a large number of clones of a young woman named Lintilla. The company's clean-up plan involves an equally large number of attractive male "anti-clones" and a set of "Agreements to Cease to Be" disguised as marriage certificates.
* UnstableGeneticCode:
-->''The Haggunenons of Vicissitus Three have the most impatient chromosomes of any life form in the Galaxy. Whereas most races are content to evolve slowly and carefully over thousands of generations, discarding a prehensile toe here, nervously hazarding another nostril there, the Haggunenons would do for Charles Darwin what a squadron of Arcturan stunt apples would have done for Sir Isaac Newton. Their genetic structure, based on the quadruple sterated octohelix, is so chronically unstable that, far from passing their basic shape onto their children, they will quite frequently evolve several times over lunch.''
* VengefulVendingMachine: Arthur Dent, sick of getting a drink which is almost, but not quite, entirely ''unlike'' tea from the Nutri-Matic machine, gives it a lengthy lecture on the nature and history of real tea. The machine hijacks the starship's entire computing power to work on the problem of why on earth someone wants dried leaves in boiling water, leaving the ship defenceless against a missile attack. Arthur gets his tea in the end, though.
* WeirdTradeUnion: The Amalgamated Union of Philosophers, Sages, Luminaries and Other Professional Thinking Persons, which opposed using the computer Deep Thought to find the Answer to the Ultimate Question of Life, the Universe and Everything because, under law, the quest for Ultimate Truth was under their prerogative, and not the computer's. They even threatened to go out on strike, though they dodged the question of who, exactly, that would inconvenience.
* WhatDoesThisButtonDo: Lampshaded.
-->'''Arthur Dent''': What happens if I press this button?
-->'''Ford Prefect''': I wouldn't--
-->'''Arthur Dent''': Oh.
-->'''Ford Prefect''': What happened?
-->'''Arthur Dent''': A sign lit up, saying "Please do not press this button again."

!!The three revived seasons contain examples of:

* AndThereWasMuchRejoicing: The final fate of Wowbagger.
* BackForTheFinale: The ending sequence of the final episode of the Quintessential Phase (and the final episode of the radio series altogether) has the return of Fenchurch and Marvin, as well as Max Quordlepleen, the Great Prophet Zarquon, Wowbagger, Lintilla, Prosser, and a few other bit players.
* BookEnds: Played with. [[spoiler: One of the alternate Earths features Arthur lying in front of a bulldozer ready to demolish his house, but Fenchurch is with him this time.]]
* ComicBookTime: The original two series, broadcast from 1978 - 1980, were intended as a contemporary piece. While the narrative quickly left Earth and there is not much to date it, it can still be a bit jarring when the [[Main/RecursiveAdaptation later three series]] have scenes on or in reference to Earth that make more modern cultural references, or include as common technology things that would not yet have been common or even have existed. Of course, when dealing with possibilities such as different versions of Earth existing across multiple planes of reality, one supposes that such things may be relative.
* ContentWarnings:
** One episode of the Tertiary Phase finishes with the warning: "The preceding program contains scenes of extreme violence which may be disturbing to some viewers. Time travellers of a nervous disposition may wish to consider listening to something else for the previous half-hour."
** Played straight when the episode featuring the destruction of the Guide offices was broadcast on [[Creator/TheBBC Radio 4]] [[TooSoon shortly after 9/11]].
* EverybodyLives: [[spoiler:All the core cast manages to survive at the very end of the series, including Trillian and her alternate self (who merge into a single being), Marvin (who was still under warranty when he expired), and Fenchurch (who had been waiting at Milliway's since she seemingly ceased to exist). And the Vogons fail to eradicate every Earth.]]
* OddlyNamedSequel: The original two series and the later adaptation of "Life, the Universe and Everything" were released as the Primary, Secondary and Tertiary Phases. The adaptations of the last two books became the Quandary and Quintessential Phases -- more accurate titles would be the Quaternary and Quinary Phases.
* {{Retcon}}: The entire Secondary Phase is AllJustADream Zaphod had, to cover for the Tertiary Phase opening with Ford and Arthur still being stranded on prehistoric Earth. [[spoiler: Subverted when Zaphod discoverss it ''did'' all happen. Inside Zarniwoop's office. [[MindScrew Meaning the time in the Secondary Phase spent in Zarniwoop's office was inside Zarniwoop's office.]]]]
* SoundDefect: In the Tertiary Phase, the insertion of the key into the Slo-time lock is interrupted by the Guide, which digresses on the subject of sound effects and why that one didn't "cut the mustard" before substituting a second sound effect.
* SoundEffectBleep: Fit the Sixteenth from the Tertiary Phase. The book ''Life, The Universe And Everything'' on which the Phase was based featured an award for "The Most Gratuitous Use of the Word Fuck in a Serious Screenplay"; since it was scheduled to be broadcast at 6.30 pm the word was still uttered by the actor but completely masked by the sound of a starship engine.
* TheFourthWallWillNotProtectYou: The final episode has [[spoiler: a bit where the radio announcer tries to reassure the audience that the Vogon ships they are seeing are only illusions.]]

!!The sixth season contains examples of:
* BackFromTheDead: Though Marvin remained dead in ''And Another Thing...'', he appears outside Arthur's shack in Episode 1 (the Sirius Cybernetics Corporation took his personality and put it in another body). Subverted when it turns out to only exist in [[LotusEaterMachine the Guide Mark II]], [[spoiler:then double-subverted in Episode 6 when Arthur finds him in the same place in reality]].
* EarnYourHappyEnding: The ending of ''Literature/AndAnotherThing'' plays out mostly as it originally does, with nearly everyone getting some sort of happy ending, but [[spoiler:Fenchurch is present at the shack (to Arthur's surprise), having filled out the permit that staves off the Vogons]]. After everything he's been through, [[spoiler:Arthur finally gets a happy ending. [[ArsonMurderAndJaywalking Oh, and Marvin lives, too]]]].
* HappyEndingOverride: It turns out that the ending of the Quintessential Phase was little more than [[LotusEaterMachine a virtual reality created by the Guide Mark II]], as a means of persuading the cast to return to Earth before its destruction -- which, by the by, is still moments away from occuring.
* OddlyNamedSequel: Just like the Quandary and Quintessential Phases, this series is the Hexagonal Phase, and not the "Senary Phase".
* SpecialGuest: The late Creator/StephenHawking provides the voice of the Guide Mark II in Episode 1. Random even [[LampshadeHanging mentions it sounds like him]], but is cut off before she says his name. The Guide Mark II even implies that in other timelines, it was the man himself.