Counting each game individually, there are currently 30 games in the series internationally, 31 in Japan, and 21 in South Korea. Counting paired individual games as a single release, there are currently 16 games in the series internationally, 17 in Japan, and 10 in South Korea.
Prior to Generation VI, it was standard for the Western releases of the core series games to include the label Version in their title, although this was seldom used by the Japanese releases. In Japanese, Korean, and Chinese, the series is called the Pocket Monsters Series (Japanese: ポケットモンスターシリーズ, Korean: 포켓몬스터 시리즈, Chinese: 精靈寶可夢系列 / 精灵宝可梦系列), as core series games all contain the full name Pocket Monsters in their title, whereas side series and spin-off games use the abbreviation Pokémon in the title instead. However, the Japanese releases of the Pokémon Stadium series use Pocket Monsters in English subtitles, despite the titles using Pokémon in kana.
While there are no strict rules that make a game a core series game, and previously assumed rules are continuously broken, the games generally have a similar plot and mechanics.
The player begins the game in a small town or city of a given region, having no Pokémon of their own. Through a course of events, the player will receive a starter Pokémon from the region's Pokémon Professor; the starter Pokémon is always a choice of three, a Grass, Fire, or Water type, and the character who will become the player's rival will typically choose (or already have) the Pokémon whose type is super effective against that of the player's choice, although some exceptions to this pattern exist.
After this point, the player begins to journey across the entire region (each with their own cities and towns, themselves connected by route), capturing any wild Pokémon he or she chooses to, and using a party he or she assembles to take on the eight Gym Leaders (except in Alola where the player battle in Trials instead) of the region. Alongside encounters with both other Trainers and repeated interactions with their rival, the player must also stop the plans of a villainous team, which often involve the manipulation of Legendary Pokémon.
After all eight Gym Leaders have been defeated, the player can enter the Pokémon League, where the Elite Four and Champion await challengers. The Champion of the region is often introduced prior to the player's Pokémon League challenge, and may aid the player as he or she continues his or her adventure.
Though the game can be considered over as soon as the player has defeated the Champion, there is still post-game content. Often there is a post-game plotline and locations and facilities that could not be previously accessed. Since Pokémon Crystal, there is usually at least one facility specifically dedicated to battling. The overarching goal is the completion of the Pokédex; after this has been done, the player will receive a diploma for completing the regional Pokédex and, starting in Generation III, another for completing the National Pokédex. Another task was added in Generation III in order to fully complete the game: obtaining all Trainer Cardstars.
Another element that characterizes a core series game is that the geography of regions includes at least one water route, a mountain, several caves, a forest, as well as a final route leading up to the Pokémon League called Victory Road.
While releases continue to break patterns, the release of core series games tends to follow a pattern.
When a generation of Pokémon games begins, a pair of games is always released. These paired versions feature virtually the same storyline as each other, but the available Pokémon differ, and some other elements are usually slightly different. This encourages trading, as it is required in order to complete the regional Pokédex.
Most generations feature an "upper version" title—often referred to by fans as a "third version"—a follow-up game or pair of games released after the first games of the generation that takes place in the same region with added features. These games typically both share and lack certain regional Pokémon that were available in one or both of the original paired versions; thus, a player of an upper version must link together with the original pair to complete the regional Pokédex as well. On the contrary, upper versions typically contain certain Pokémon from different regions that are unavailable in the original pair, thus being more helpful in completing the National Pokédex. Until Generation VII, only a single third version following an original pair was ever released at a time; Pokémon Ultra Sun and Ultra Moon were the first games to be released as a pair. Unlike other generations, Generation V opted for a sequel story instead, and Generation VI entirely forewent follow-up games set in the same region.
Sometimes, a secondary set of paired versions that are remakes of earlier titles may also be released.
In all generations, there are some Pokémon that cannot be encountered until after the player enters the Hall of Fame. These may be legendary Pokémon, such as Mewtwo, or simply Pokémon that are not part of the game's regional Pokédex.
Before the release of a new generation, new Pokémon are often used to promote the new games by including them in the anime or in spin-off games.
The box art for each game features one Pokémon which was introduced in that generation (or, in the case of remakes, the generation of the original games). This Pokémon is referred to by fans as a game mascot, and with the exception of Kanto-based games, it is always the Legendary Pokémon available in that game at the climax of the storyline.
In terms of the artwork itself, the international Pokémon Red and Blue and all region releases of the initial paired games of each generation from Generation III to VII use their game mascot's original Ken Sugimori artwork for their box art, whereas all other core series games use specially made artwork.
Several pieces of content in the core series Pokémon games depend on the games having a timeline, but a complete timeline cannot be drawn from the games themselves. On May 7, 2014, Game Freak employee Toshinobu Matsumiya's Twitter account posted a timeline of the core series Pokémon games; the tweet was subsequently deleted.
Contrary to what is sometimes reported, the name WaterBlue was not trademarked by Nintendo, Creatures, or Game Freak. According to the Japan Platform for Patent Information, ウォーターブルー and WATER BLUE (application number 2010-060625, registration number 5386853) are trademarks of Meiji Seika, a Japanese pharmaceutical company. However, Game Freak's Junichi Masuda did mention "WaterBlue" in 2004 on a blog post explaining the company's choice of "FireRed" and "LeafGreen" as both Japanese and international titles for the remakes of Red and Green.
In addition to the core series games, each of the side series games allow players to transfer their Pokémon to and from the core series:
Pokémon Stadium: Allows players to transfer their Pokémon from the Generation I core series games to battle in 3D.
Pokémon Stadium 2: Allows players to transfer their Pokémon from the Generation I and II core series games to battle in 3D.