Which Pokémon generation introduced the largest number of new species, with 156?

Generation V introduced the largest number of new Pokémon species, with 156.

The generation debuted in Pokémon Black and White for the Nintendo DS in 2010. Its new species were numbered from Victini at National Pokédex #494 through Genesect at #649, making the fifth generation the largest single addition to the main series.

Generation V made a notable design choice: the original Pokémon Black and White games largely restricted the main story to newly introduced species. Older Pokémon became available more broadly after the story, giving the Unova region a distinct identity and encouraging players to learn the new roster.

The total is sometimes confused with the number of Pokémon available in a particular game. “156” refers to species introduced by the generation, not every creature obtainable in Black and White. The generation also includes sequels and related releases, but the record is based on the new species introduced in the generation.