The Pokédex is the official encyclopedia of Pokémon species in the Pokémon world.
Professor Oak gives the protagonist a Pokédex in the original games, asking the player to record information about every Pokémon encountered. Catching a species usually registers its full entry, while seeing one records a limited entry. The device therefore turns the adventure into a collection and research project as well as a series of battles.
Different regions use local Pokédexes containing species native to that game’s setting. The National Pokédex combines species from across regions, although not every game includes every species. In the anime, Pokédexes are handheld electronic references that provide descriptions and identification during journeys.
Pokédex is a portmanteau of “Pokémon” and “index.” It is not the same as Pokégear, PokéNav, or Pokétch, which are multifunction devices used in particular games.