Generation I’s original National Pokédex included 151 Pokémon species. The list runs from Bulbasaur at number 001 to Mew at number 151.
These species were introduced through the first-generation games, beginning with Pocket Monsters Red and Green in Japan in 1996. International versions were released as Pokémon Red and Blue, and players were encouraged to trade between versions because each game contained species unavailable in the other.
The total is often remembered incorrectly as 150 because Mew was difficult to obtain and was not normally encountered during the standard story. However, Mew is National Pokédex number 151 and is part of the original generation. MissingNo., a famous glitch Pokémon-like entry, is not an official species and does not increase the canonical total.