Pokémon Blue is the third core series Pokémon game released as a minor revision of Pokémon Red and Green, which were released earlier that year. It was thus the first solitary version in the core series of Pokémon games. Various fixes in the game include a graphics and sound upgrade, as well as the removal of several known glitches that had been found in the original pair. Outside of Japan, its graphics, game engine and script formed the basis of Pokémon Red and Blue, while the wild Pokémon and game-exclusive Pokémon lists were changed to match Red and Green.

The player character starts out in Pallet Town. When the player character tries to leave the town without a Pokémon of their own, they are stopped in the nick of time by Professor Oak, who invites them to his lab. There, he gives them a Pokémon of their own and a Pokédex, telling them about his dream to make a complete guide on every Pokémon in the world. After the player character battles their rival and leaves the lab, they are entitled to win every Gym Badge, compete in the Pokémon League, and fulfill Oak's dream by catching every Pokémon.