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A classic role-playing game originally created by TSR, the same people who made ''DungeonsAndDragons''. Centuries after a vaguely defined apocalypse, a radioactive and ruin-strewn Earth is inhabited by mutants, sentient animals and plants, and insane half-functioning robots, all of whom compete for influence as multi-species civilization begins its long climb to recovery. ''Gamma World'' was heavily influenced by TSR's earlier sci-fi RPG, ''Metamorphosis Alpha''.

Despite what a newcomer might think, the tone is quite light-hearted, and the players are strongly encouraged to have fun and not think too hard about how silly it all is.

The game has gone through seven editions so far; TSR published the first three from 1978 to 1985 with their own unique rule sets. 1992's 4th Edition was based on the same engine as ''D&D'''s 2nd edition, and 1995's 5th was a supplement for the sci-fi RPG ''TabletopGame/{{Alternity}}''. In 2002, WizardsOfTheCoast, which had since absorbed TSR, published a wacky homage to ''Gamma World'' entitled ''Omega World'' in ''Polyhedron'' magazine.

The setting was licensed by Sword & Sorcery Studios (a subsidiary of WhiteWolf) and heavily revised for ''{{d20 Modern}}'' in 2003. This new edition recasts the apocalypse as a war among post-[[TheSingularity Singularity]] civilizations, a horrific spasm of nanotechnological and biological warfare (with a few nukes thrown in for old time's sake). The old creatures and robots are nearly all retained, but given new and detailed explanations that are designed to elicit horror and awe rather than cheap jokes.

WizardsOfTheCoast has since released a seventh edition of ''Gamma World'', using the 4th edition ''DungeonsAndDragons'' rules, in October 2010. The game is far more humorous, from character creation, to Omega Tech descriptions. The 7th Edition setting is one where "the Big Mistake" merged all possible worlds into one, and really leaves the door open for player interpretation.

''Gamma World'' is notable for one rather odd trend: usually, only a handful of books would be released before a new edition came out and rendered all the previous books obsolete. This reached its zenith with the ''TabletopGame/{{Alternity}}'' version, which had only a single, core rulebook released before being discontinued. Time will tell if 7th Edition will continue this trend.

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!!This game includes examples of:

* AdamAndOrEve
* AdaptationDistillation: ''[[D20Modern Omega World]]'', a tribute to the original game.
* AdventureTowns
* AfterTheEnd
* AmazingTechnicolorPopulation: Antimatter Blasters are blue, Demons are red, and Photonics come in shiny red, blue, or green.
* AmmunitionBackpack: Contained an atomic energy cell that powered the fusion rifle.
* AncientConspiracy
* ApocalypseHow: Class 2
* ArtisticLicensePhysics
* AttackItsWeakPoint: Adventure [=GW1=] ''Legion of Gold''. An amoeboid monster' body can withstand 1,000 HitPoints of damage, but its nucleus can only take 50 HitPoints before it's killed.
* AtomicSuperpowers
* AutoDoc: The 1st Edition Medi-Kit
* [[BeastMan Beast Men]]
** BigCreepyCrawlies: Cockroaches and Arachnoids.
** BigfootSasquatchAndYeti: Yetis.
** EverythingsBetterWithMonkeys: Simians.
** EverythingsSquishierWithCephalopods: Octopoids.
** LizardFolk: Saurians.
** WingedHumanoid: Hawkoids
* BrainInAJar: Borgs, Permanent Cybernetic Installations and Think Tanks in 1st Edition.
* ChameleonCamouflage: The Chameleon Powers mutation in the 1E game.
* CityInABottle
* CollectibleCardGame: 7th edition has its powers and technology sold on this model; [=GMs=] and players have to buy more cards in booster packs for more fantastic stuff to use in their RPG, instead of buying them in sourcebooks. [[InternetBackdraft This has not been well received.]] However, the core game ''does'' include include a full deck of mutations and Omega Tech (Loot), so players aren't forced to go out and buy boosters. The boosters certainly don't have anything that's any more game-breaking than what you get in the core box.
* CrapsackWorld
* CrystalDragonJesus
* DarkerAndEdgier
** The 6th Edition for ''{{d20 Modern}}''.
** The original game when it first came out. It's said to have popularized dark humor in [=RPG=]s.
* DashAttack: In the adventure [=GW6=] ''Alpha Factor'', the mutant creatures known as the S're'daan and the Ba'crolbai would [[HornAttack attack opponents with their horns]] after charging into them.
* DuctTapeForEverything: We're sure you'll find a use for this...
* [[BearsAreBadNews Everything's Worse With Bears]] [[ItMakesSenseInContext Who Think They Are Napoleon]]
* FantasticRacism: The Knights of Genetic Purity, the Iron Society, the Zoopremicists...the list goes on.
* FungusHumongous: Adventure [=GW1=] ''Legion of Gold''. The buggem lair has a room filled with a fungus garden made up of tall, shrub-like fungi.
* HomeFieldAdvantage: The adventure ''[=GW6=] Alpha Factor''. Jeremiah Coot has filled his base Mindkeep with all sorts of traps, including false vines that cause any opponent who tries to swing on them to fall.
* HornAttack: Mutant characters could have horns as a mutation. The mutants known as Rakoxen (and Hoppers in 2nd Edition) had them. Two new monsters in the adventure [=GW6=] ''Alpha Factor'', the S're'daan and the Ba'crolbai, had horns that they could use to attack opponents after [[DashAttack charging into them]].
* HorseOfADifferentColor: Mutant horses, giant horses, podogs, ''cactus horses''...
* ILoveNuclearPower
* ImprobableWeaponUser: Since the game is set in a ScavengerWorld, it is almost a given that your characters will be these. You could wield a stop sign, a telephone pole, vending machines...really anything you can think of that fits within the one-handed/two-handed light/heavy melee/ranged parameters.
* KillerRobot: Technically could be your player character. The Created are an entire faction made of Killer Robots.
* LightEmUp: Photonic origins.
* LostTechnology
* MachineWorship
* MakeMeWannaShout: The 1E Sonic Attack Ability mutation.
* TheMultiverse: The seventh edition backstory features the Large Hadron Collider causing several different realities to intermingle and exchange places, in an event called "the big mistake". Furthermore, Dopplegangers create their doubles by pulling them out of alternate realities.
* {{Mutants}}
* NanoMachines
* NinjaPirateZombieRobot: Because you can choose two origins for your character, and the origins are each quite different, you can end up with lots of these. Android Plants, Vampire Octopoids, a hoard of tiny yetis...
* OverclockingAttack: Alpha mutations have this option, with a 45% chance of failure.
* PlantPerson
* PlayingWithFire
* PsychicBlockDefense
* RadiationImmuneMutants: Notably averted. While there were mutations that allowed for resistance to radiation, it wasn't universal to all mutants.
* RagnarokProofing
* RecycledINSPACE: It's ''D&D'', but [-[[AfterTheEnd AFTER THE END]]-]! [--[[SlidingScaleOfSillinessVersusSeriousness AND SILLY]]--]!
* RuleOfCool
* RuleOfFun
* ScavengerWorld
* ShroudedInMyth: The world before the Cataclysm. Old technology are known as artifacts, electricty is called lightning and machinery, particularly robots, are called live metal.
* SicklyGreenGlow
* SlidingScaleOfSillinessVersusSeriousness
** The original game, 4th edition, and ''Omega World'' are so far on the silly scale that it mutates and flies out into space. 3rd edition and 6th edition, on the other hand, land on the more serious part of the scale, but not to the very end.
** 7th Edition is much closer to the silly end, including a suggestion that you could respond to a villain by pulling out a cane and singing and dancing like Michigan J. Frog, a backstory in which Peshtigo, Wisconsin suffered nuclear annihilation by the French an untold number of times over (it's said to have happened in 3% of the originally-separate universes that combined into Gamma Terra), random shout-outs to virtually everything under the sun, and not even an attempt to make the yexil (Basically cloth-eating anthropomorphic manticore bandits with laser eyes--no, really) or the other more bizarre monsters anything except completely ridiculous.
* SlidingScaleOfTurnRealism: Round by Round.
* SpareBodyParts
* SuperPoweredRobotMeterMaids: Literally.
* SuperSpit: Several ''Magazine/{{Dragon}}'' magazine articles gave new mutations and mutants with this ability, and the Bu'daan in [=GW6=] ''Alpha Factor''.
* SwissArmyWeapon: The Chameleon Rifle in module [=GW6=] ''Alpha Factor''.
* TheWormThatWalks: One of the possible character origins. Depending on your primary origin and your secondary origin, you could be anything from a horde of cockroaches, to a [[GreyGoo mass of nanomachines]], to a horde of ''[[CuteKitten sentient, hive-minded kittens]]''.
* UniversalAmmunition: The 7th edition uses an abstract system of ammunition, where any weapon can use any type of ammo. However, using more than one shot per encounter will cause you to run out.
* VampiricDraining: Adventure [=GW1=] ''Legion of Gold''. In the buggem lair, the parn embryots will jump onto victims' heads or shoulders, bite them and suck out their bodily fluids at a rate of 10 HitPoints per combat round.
* WetwareCPU: Androids. Inverted with AIs.
* WhenTreesAttack: Plants are a possible character origin in all of the editions. Also there have always been numerous species of plant-monsters to spice up wilderness adventures.
* XMeetsY: D&D meets VideoGame/{{Fallout}}. (Although, chronologically speaking, ''Fallout'' is actually ''Gamma World'' meets ''Mad Max.)''
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