Generation I of the Pokémon video game series contains 151 species.
These original species debuted in the 1996 Game Boy games Pokémon Red, Green, and Blue. Their National Pokédex numbering runs from Bulbasaur at 0001 to Mew at 0151.
The number 150 can cause confusion because Mew is often treated as a secret or Mythical Pokémon discovered after the main game adventure. Mew is nevertheless part of Generation I and occupies National Pokédex position 0151.
Regional releases also created naming confusion. The Japanese originals were Red and Green, while most international markets received Red and Blue. Both versions belong to the same first generation and share the original set of 151 species.