The original Generation I Pokédex contained 151 Pokémon species.
Those species debuted in the 1996 Pokémon Red, Green and Blue games, with Pokémon Yellow following later. The Kanto Pokédex numbers run from Bulbasaur at No. 001 through Mew at No. 151, although Mew was distributed as a secret event Pokémon rather than normally encountered.
Many players remember 150 because Mewtwo is the final regularly obtainable species in the games. Mew, numbered 151, was hidden from ordinary gameplay and became famous through special Nintendo events and the first movie.
Later generations expanded the national roster dramatically, but the number 151 remains central to the franchise’s slogan and 30th-anniversary nostalgia. Regional Pokédexes can contain fewer species, while the National Pokédex tracks Pokémon introduced across generations.