In the anime, during evolution, a Pokémon will become surrounded by a light and slowly change shape. From Pokémon the Series: The Beginning through to Pokémon the Series: Diamond and Pearl, the Pokémon is surrounded by a white light, while in Pokémon the Series: Black & White to Pokémon Journeys: The Series, the Pokémon is surrounded by a golden or blue light. An evolution can also occur through multiple Pokémon of the same species combining.
To some Pokémon, evolution means growing up, while to others, it just refers becoming another species or getting upgraded. However, many of them retain the memories of their life during their pre-evolution form. Evolution in the Pokémon games is more similar to metamorphosis (the process certain bugs undergo to become an adult) than actual evolution (a long process that happens to populations of creatures).
Pokémon gain experience after battling wild Pokémon and Pokémon Trainers. After gathering enough experience points, the Pokémon levels up. When a Pokémon reaches a particular level, it will evolve into its next form (if it has one). There are ways to share experience, such as allow a Pokémon to hold Exp. Share: a hold item that allows the user to earn experience even if it did not participate in the battle.
Evolution can be prevented by simply press the 'B' button on the Game when the Pokémon is attempting to evolve. This is useful as some Pokémon will learn moves that cannot be learnt in a later form or if you want a Pokémon to learn a move earlier than usual. For example, Gabite. If you let Gible evolve into Gabite at level 24 it will learn Dragon Rush at level 49, but if you keep Gible it will learn Dragon Rush at level 37. Sometimes it doesn't matter if you let it evolve or not. The Pokémon can hold an Everstone, which keeps them from evolving, so that you don't have to keep cancelling the evolution every time the Pokémon levels up. Although some Pokémon can evolve more than once (Poliwhirl, Cascoon, etc.), some basic Pokémon just can't evolve, due to undiscovered forms, or if they are really rare (Chatot, Groudon, etc.). There are also Pokémon that can evolve into different things like love, choice, etc. (e.g. Eevee, Poliwhirl, Wurmple, or Kirlia)
Some Pokémon will not evolve unless you use special items, mostly consisting of Evolutionary Stones, which are linked to the Pokémon's type. Here are a list of Pokémon that can evolve by giving them the items.
Held item evolutions
Some items are needed for a Pokémon to evolve. If a Pokémon hold the item allowing it to evolve, let it level up once and it will then evolve into the second form.
|Gligar||Held Item: Razor Fang at Night||Gliscor|
|Sneasel||Held Item: Razor Claw at Night||Weavile|
|Sneasel (Hisuian)||Held Item: Razor Claw at Day||Sneasler|
|Happiny||Held Item: Oval Stone at Day||Chansey|
Trading and held item evolutions
A small group of Pokémon refuses to evolve, no matter if you are at the appropriate level to trigger the evolve process, unless you trade them with a friend. Some Pokémon need to have a held item to evolve when trading with a friend. Another group require specific Pokémon to be trade in order to evolve. In Pokémon Legends: Arceus, Pokémon that would evolve by being traded are instead evolved with a Linking Cord. Pokémon that would evolved while being traded and holding a certain item are evolved by being exposed to the item directly without needed to be traded.
|Kadabra||None/Linking Cord in Legends:||Alakazam|
|Graveler (Alolan)||Golem (Alolan)|
|Onix||Held Item: Metal Coat||Steelix|
|Poliwhirl||Held Item: King's Rock||Politoed|
|Seadra||Held Item: Dragon Scale||Kingdra|
|Porygon||Held Item: Upgrade||Porygon2|
|Clamperl||Held Item: Deep Sea Scale||Gorebyss|
|Held Item: Deep Sea Tooth||Huntail|
|Electabuzz||Held Item: Electirizer||Electivire|
|Magmar||Held Item: Magmarizer||Magmortar|
|Rhydon||Held Item: Protector||Rhyperior|
|Porygon2||Held Item: Dubious Disc||Porygon-Z|
|Feebas||Held Item: Prism Scale (Generation V-)||Milotic|
|Dusclops||Held Item: Reaper Cloth||Dusknoir|
|Shelmet||Trade for Karrablast||Accelgor|
|Karrablast||Trade for Shelmet||Escavalier|
|Spritzee||Held Item: Sachet||Aromatisse|
|Swirlix||Held Item: Whipped Dream||Slurpuff|
Small groups of Pokémon requires a gender to evolve into the next stage.
|Kirlia||Dawn Stone (♂ - Male)||Gallade|
|Burmy||Level 20, (♀ - Female)||Wormadam|
|Level 20, (♂ - Male)||Mothim|
|Combee||Level 25, (♀ - Female)||Vespiquen|
|Snorunt||Dawn Stone , (♀ - Female)||Froslass|
|Salandit||Level 33, (♀ - Female)||Salazzle|
Certain Pokémon, especially baby Pokémon, requires friendship with its trainer and if they are fond enough, they are willing to evolve. Some Pokémon only evolves in a certain time of the day with friendship.
|Meowth (Alolan)||At Night||Persian (Alolan)|
Special Pokémon evolve by leveling up at a certain area of location.
|Magneton||Locations with an Special Magnetic Field
|Eevee||Locations with an Moss Rock
|Locations with an Ice Rock
Certain Pokémon need to know a move to evolve. This method was introduced in Generation IV, starting with Diamond/Pearl/Platinum.
|Tangela||Learning Ancient Power||Tangrowth|
|Mime Jr.||Mr. Mime|
|Aipom||Learning Double Hit||Ambipom|
|Poipole||Learning Dragon Pulse||Naganadel|
The current time of day will sometimes affect evolution. This method was introduced in Generation VI, starting with X/Y/OR/AS.
|Ursaring (Hisui)||Expose to a Peat Block during a full moon||Ursaluna|
|Tyrunt||Level 39+ during the day.||Tyrantrum|
|Amaura||Level 39+ during the night.||Aurorus|
|Rattata (Alolan)||Level 20+ during the night.||Raticate (Alolan)|
|Cubone (Alola)||Level 28+ during the night.||Marowak (Alolan)|
|Yungoos||Level 20+ during the day.||Gumshoos|
|Rockruff||Level 25+ during the day.||Lycanroc (Midday)|
|Level 25+ during the night.||Lycanroc (Midnight)|
|Level 25+ during the dusk with Own Tempo Ability.||Lycanroc (Dusk)|
|Fomantis||Level 25+ during the day.||Lurantis|
|Linoone (Galarian)||Level 35+ at night.||Obstagoon|
Some Pokémon have unique ways of evolving.
|Farfetch'd (Galarian)||Get 3 Critical Hits in 1 Battle||Sirfetch'd|
|Eevee||2+ Affection in Pokémon-Amie or Pokémon Refresh/Has high friendship, learn a -type move.||Sylveon|
|Wurmple||Level 7 (Random depending on PV - Personality Value)||Silcoon|
|Qwilfish||Use Barb Barrage twenty times in Strong Style||Overqwil|
|Stantler||Use Psyshield Bash twenty times in Agile Style||Wyrdeer|
|Tyrogue||Level 20, Attack stats more than Defense||Hitmonlee|
|Level 20, Defense stats more than Attack||Hitmonchan|
|Level 20, Attack stats equal to Defense||Hitmontop|
|Feebas||Maxed out Beauty Condition and then level up (Generation III - IV)||Milotic|
|Nincada||Level 20, with empty Poké Ball and an open slot on your party.||Shedinja|
|Mantyke||Level up with a Remoraid in the party.||Mantine|
|Basculin (Hisui)||Lose at least 294 HP from recoil damage, not counting damage that results in it fainting||Basculegion|
|Yamask (Galar)||Walk under the stone bridge in Dusty Bowl after Yamask has taken at least 49 HP in damage without fainting.||Runerigus|
|Pancham||Level 32+ with a -type in your party.||Pangoro|
|Inkay||Level 30+ while holding the Nintendo 3DS upside down/the Nintendo Switch upside down in handheld mode when disconnecting the Pro Controller by removing the Switch from the docking station.||Malamar|
|Sliggoo||Level 50+ during rainy or foggy weather.||Goodra|
|Cosmoem||Level 53+ in Pokémon Sun, Ultra Sun, or Sword.||Solgaleo|
|Level 53+ in Pokémon Moon, Ultra Moon, or Shield.||Lunala|
|Meltan||Evolve in Pokémon GO once the player has 400 Meltan Candies.||Melmetal|
|Toxel||Level 30+ with Bashful, Bold, Calm, Careful, Gentle, Lonely, Mild, Modest, Quiet, Relaxed, Serious, or Timid Nature.||Toxtricity (Low Key)|
|Level 30+ with Adamant, Brave, Docile, Hardy, Hasty, Impish, Jolly, Lax, Naive, Naughty, Rash, Quirky, or Sassy Nature.||Toxtricity (Amped)|
|Milcery||Spin clockwise for 5 seconds during the day, holding a Sweet||Alcremie (Vanilla Cream)|
|Spin counter-clockwise for 5 seconds during the day, holding a Sweet||Alcremie (Ruby Cream)|
|Spin clockwise for 5 seconds during the night, holding a Sweet||Alcremie (Matcha Cream)|
|Spin counter-clockwise for 5 seconds during the night, holding a Sweet||Alcremie (Salted Cream)|
|Spin clockwise for more than 5 seconds during the day, holding a Sweet||Alcremie (Caramel Swirl)|
|Spin counter-clockwise for more than 5 seconds during the day, holding a Sweet||Alcremie (Ruby Swirl)|
|Spin clockwise for more than 5 seconds during the night, holding a Sweet||Alcremie (Lemon Cream)|
|Spin counter-clockwise for more than 5 seconds during the night, holding a Sweet||Alcremie (Mint Cream)|
|Spin counter-clockwise for more than 10 seconds during the dusk/dawn, holding a Sweet||Alcremie (Rainbow Swirl)|
|Kubfu||Complete the Tower of Darkness||Urshifu (Single Strike Style)|
|Complete the Tower of Waters||Urshifu (Rapid Strike Style)|
- Main article: Mega Evolution
Certain Pokémon will be able to Mega Evolve with the use of a Mega Stone, a held item, if its Trainer has a Key Stone. However, the Pokémon will revert into their non-Mega Evolved form at the end of the battle, or after the Pokémon faints.
- Main article: Primal Reversion
Primal Reversion is a similar state to Mega Evolution, but the Pokémon devolve to a previous state in the past.
It is a possible game mechanic in Pokémon Omega Ruby and Alpha Sapphire, most likely because this mechanic was founded during development of Pokémon Omega Ruby & Alpha Sapphire.
Devolution is a form of reverse evolution when a Pokémon reverts to a previous state. The only instance devolution happens in the games is in Pokémon Super Mystery Dungeon, in which the player Pokémon and partner Pokémon evolve and soon devolve three times during the main story, and Pokémon Mystery Dungeon: Gates to Infinity, which includes the Devolve Orb that devolves all enemies in the room.
Devolution is common in the Manga and TCG. It is achieved mainly unnaturally—through experimentation, or Devolution Spray. Though certain Pokémon, such as Isamu's Clefairy and Pikachu are capable of devolving themselves. The TCG also has it that Eeveelutions can revert into Eevee and that Mew has two special attacks named the Devolution Beam and Devo Crush - both of which which devolves the Pokémon hit by the attack. Golurk and Jirachi also possess special attacks which allow them to devolve an opposing Pokémon.
- There are eight Pokémon that can evolve into two different Pokémon, but only two that evolve into more: Tyrogue (three) and Eevee (eight).
- As of Generation VIII, there are 87 Pokémon that do not evolve in any way. This is discounting Legendary Pokémon, Mythical Pokémon, and form changes such as Mega Evolution.
- In "Dream a Little Dream from Me!", there is a group of Pokémon who evolved and devolved unnaturally, one actually missing its second evolved form.
- In Final Rivals!, an evolution has occurred through multiple Pokémon of the same species combining, which was shown by Ash's Meltan and its horde.
- Larvesta evolves at the highest level out of all unevolved Pokémon so far (level 59).
- Zweilous evolves at the highest level out of any evolved Pokémon so far (level 64).
- Porygon is currently the only Pokémon to be able to evolve at level 1 into both its evolutions, as they do not need a certain level to evolve.
- Generation VII was the first generation to introduce Legendary and Mythical Pokémon capable of evolution.
- Poipole is the only Ultra Beast that can evolve.