The first generation introduced 151 Pokémon species.
These species debuted in Pokémon Red, Green, Blue, and Yellow and occupy National Pokédex numbers 001 through 151. Bulbasaur begins the numbered list, while Mew is number 151.
The count is often confused because Mew was a secret Mythical Pokémon added late in development and was not normally available through ordinary gameplay. Some players therefore remember the original games as having 150 obtainable Pokémon, while the complete first-generation roster contains 151 species.
The first-generation total remained a defining milestone for the franchise. Later generations added new regional creatures while retaining many older ones. The National Pokédex eventually became a way to organize Pokémon from multiple generations, but the original 151 remain the most closely associated with Pokémon’s 1990s debut.