Gender

The gender (Japanese: ''' ') of a is a concept introduced in Generation II, though touched upon in Generation I. In, most species of Pokémon were assigned a gender, male (Japanese: オス male) or female (Japanese: メス female); however, the genders of some species of Pokémon were left unknown (Japanese:  unknown). This feature allowed for Pokémon breeding, as well as introducing the concept of a Pokémon Egg to the series. Gender makes no difference in the stats of a Pokémon after Generation II, unless the two Pokémon are a different species entirely, such as Nidoran.

In, a choice of between a male (Japanese: ' male) and female (Japanese: ' female) player character became available for the first time. However, both men and women have been featured in the Pokémon games since Generation I.

Gender differences
Generation IV premiered minimal differences in sprite between two Pokémon of the same species. For example, a male will have the full tail seen in previous games, while the female is missing the very tip of it. Generations V and would introduce Pokémon with more drastic differences in appearance.

The only Pokémon with gender differences that are not just aesthetic is, which has different learnsets and depending on its gender. The male Meowstic has and the female Meowstic has  as its Hidden Ability. Furthermore the male Meowstic learns mostly status moves, with all of its gender-exclusive moves being status moves, while at the same levels, the female Meowstic learns mostly special moves, with only one of its gender-exclusive moves,, being a status move. Below are Meowstic's learnsets.

Related species
The Nidoran family is a special case in terms of gender. Introduced in Generation I, before gender was known for all Pokémon, and  are considered separate species of Pokémon and indeed have many differences, from appearance to moveset. However, Nidoran Eggs have a 50/50 chance of hatching into either Nidoran♀ or Nidoran♂.

In a manner similar to, Eggs produced by may hatch into. While and  are in the  in the games, likely due to being Legendary Pokémon, Latias have produced Eggs containing  in the anime, confirming that they are similarly related.

Gender-based evolutions
Some Pokémon may have different ways of evolving depending on their gender. These Pokémon may therefore have one or more evolutions that can only be a single gender.

Other single-gender Pokémon
The following is a list of all Pokémon that are either 100% male or 100% female and have not been mentioned in an above section. In particular, these Pokémon have no explicit relation to a Pokémon of the opposite gender through evolution or breeding, although some of them may have a counterpart such as with and.

In battle
The is more effective when catching Pokémon that are of the same/opposite gender of the player's Pokémon.

The following moves are dependent on gender:

The following Abilities are dependent on gender:

In Pokémon Mystery Dungeon: Explorers of Time and Explorers of Darkness and Pokémon Mystery Dungeon: Explorers of Sky, a male Pokémon has increased critical hit ratio. A female Pokémon has increased evasion.

In the games
Starting in, undefineds were given the option of choosing to play as a boy or girl Trainer at the start of the game. Since then, every game in the main series has included that choice. Starting in, the opposite-gender player character can also be encountered in the game.

Some Trainer classes have male and female variants, such as s, while others appear to be counterparts, such as s and s. Others, such as Kimono Girls, have no opposite-gender counterpart.

Certain in-game events may differ depending on the player character's gender. For example, in Pokémon Black 2 and White 2, Curtis will be encountered if the player is female, and Yancy if the player is male. In and Generation VII, availability of different clothing is gender-specific. Also, only the female player character has the option of changing their lip color using lipstick stored in a Makeup Bag in Generation VII.

In side games
Many side games in the Pokémon franchise allow the player to choose between a male or female player character as well.

In the anime
In Kanto, O-Hina Town hosts a female-exclusive tournament during the annual Princess Festival. Porta Vista hosts a beauty pageant for women only, known as the Beach Beauty and Pokémon Costume Contest. In Kalos, Pokémon Performers are exclusively female, as only girls may participate in Pokémon Showcases.

Trivia

 * In Generation II, a Pokémon's gender was determined through its Attack IV. Due to this, a female Pokémon could never have a maximized Attack stat (unless they were a member of an, such as ), because female Pokémon were given the lower portion of the IV range. This also prevented female Pokémon of a , such as starter Pokémon or , from being , due to that also being based partly on the Attack IV. From Generation III onward, neither of these traits are determined by IVs, allowing for Pokémon species with two genders to have females with maximized Attack and simultaneously retain their chances of being Shiny.
 * Although its English and French names suggest that it is exclusively male, may be of either gender. This is due to the fact that it was given its name prior to the introduction of gender to the series.
 * Since has a different gender ratio than  and, one in three female Azurill will be male after evolving into Marill, dependent on the personality value of the Azurill in question, though this no longer happens in Generation VI.
 * In the international versions of Generation II, due to how the battlefield display is programmed, Nidoran♂ and Nidoran♀ have their gender icon shown twice, once in their name, and once after the level. This does not occur in the Japanese and Korean games, however, as the gender icon was present after all Pokémon's names due to the shorter character limit there. This was addressed in all later generations, which prevent the gender icon from showing up when an un-nicknamed Nidoran of either gender is on the field.
 * In Pokémon Mystery Dungeon: Explorers of Time and Explorers of Darkness and Pokémon Mystery Dungeon: Explorers of Sky, the gender of a wild Pokémon in a dungeon is determined by the current number of floor the player stands on. If the number is odd, all wild Pokémon that can be male will be male; if it is even, all wild Pokémon that can be female will be female.