Pokémon Red and Blue featured 151 Pokémon in the original Pokédex.
The first generation introduced the species numbered 1 through 151, from Bulbasaur to Mew. Players could encounter, battle, evolve, trade, or receive these Pokémon while exploring the Kanto region.
Although the games are often described as having 150 Pokémon, that usually refers to the main obtainable species before Mew is counted. Mew was numbered 151 and was distributed through special Nintendo events, making it unusually difficult to obtain during the games’ original era.
Trading was essential because no single version contained every Pokémon. Red and Blue had version-exclusive species, so completing the Pokédex required connecting two Game Boy systems with a Game Link Cable or obtaining Pokémon through other players.