Evolution/Methods of evolution

The various triggers for a Pokémon's evolution are almost as varied as the Pokémon themselves, and some Pokémon have a unique evolution method. The most common of them is Evolution by leveling up at or above a certain level. Other methods include the following:
 * leveling up when friendship has reached a high level (220 or greater)
 * leveling up while holding an item
 * leveling up while knowing a certain move or a move of a certain type
 * leveling up in a certain location
 * trading the Pokémon
 * trading the Pokémon while holding an item
 * trading the for specific
 * using an evolutionary stone on it
 * leveling up with a certain Pokémon or Pokémon of a certain type in the party
 * leveling up while the Nintendo 3DS is upside-down
 * level up or high friendship based on time of day
 * level up a during certain types of weather.
 * being fed 400 Meltan Candy in Pokémon GO.

All evolutions via leveling up take place at the end of a, or when a Pokémon is given a Rare Candy. Each Pokémon may evolve only once per battle.

Additionally, holding an Everstone prevents a Pokémon from evolving. Surprising a Pokémon via the B Button also prevents evolution, but only for Pokémon that evolve upon gaining a level. This method is known as an "Evolution cancel".

Pokémon that faint during a will evolve at the end of that battle if its requirements have been met. However, before Generation VI, losing a battle would make Pokémon not evolve even if the conditions have been met.

In Pokémon FireRed and LeafGreen, Pokémon whose evolved forms are known in-game but not in its regional Pokédex will fail to evolve, even if the conditions have been met. For example, will fail to evolve into, a Pokémon that was already known, unless the National Pokédex is obtained.

Pokémon that can evolve into more than one Pokémon will usually have the ways in which the evolution is activated being slightly similar, such as having both being initiated by evolutionary stone or by trading while holding an item. Closely-related Pokémon, such as and, will also have very similar, if not identical, evolution methods.

Some Pokémon have different evolutions depending on their gender. For example, only female can evolve into ; male Combee cannot evolve at all. Meanwhile, all can evolve into, but female Snorunt have the option of evolving into  instead. This instance occurs in a similar way with, albeit with males having split evolution instead.

Also, there have been situations in which the current party must be configured in a specific manner for some Pokémon to evolve. So far, only three Pokémon need to have these special requirements. will evolve into if leveled up with a  in the player's party. will evolve into when it reaches level 20. However, if there happens to be an empty space in the player's party (and a spare in Generation IV onward), a  will also appear in the party. evolves into if its level is 32 or higher and there is a Dark-type Pokémon in the player's party.

Some Pokémon evolve in other unique ways. If one trades a for a, they will evolve into  and , respectively, though neither will evolve if one of them holds an Everstone. When reaches level 30, the player must hold the 3DS upside-down for it to evolve into. Also introduced was a weather-based evolution: will evolve into  beginning at level 50 only if it is raining in the area that the player is in. Finally, can only be obtained by leveling up an  that knows any  moves and has at least two hearts of Affection.

In Pokémon Sun, Moon, Ultra Sun, and Ultra Moon, Alolan Pokémon and Pokémon that evolve into Alolan Pokémon have a different theme and a different colored background during evolution.