The first-generation Pokémon games introduced 151 Pokémon species.
Pokémon Red and Green launched the series in Japan in 1996 with a collectible roster running from Bulbasaur, National Pokédex number 001, to Mew, number 151. The games made capturing, training, battling, and trading the central activities of the adventure.
The number 151 is associated specifically with the original National Pokédex, not with every Pokémon available in each individual version. Red and Green had version-exclusive species, so players needed trading to complete the collection. Mew was also unusually difficult to obtain because it was hidden in the game data and was distributed through special events.
A common mix-up is confusing the first-generation total with the number visible in one game. The original games contain 151 species across the generation, while later generations expanded the Pokédex substantially. This milestone helped define the franchise’s early slogan, “Gotta Catch ’Em All.”