From Bulbapedia, the community-driven Pokémon encyclopedia.
If you were looking for the TCG expansion released to commemorate the 20th Anniversary, see Generations (TCG). If you were looking for the animated miniseries, see Pokémon Generations.
A generation is a grouping of the Pokémon games that separates them based on the Pokémon they include. In each generation, a new set of Pokémon, region, moves, and Abilities that did not exist in the previous generation are released.
While generations are not usually discussed officially, they are occasionally. Junichi Masuda has referred to the fourth generation on his Twitter profile and sixth generation on his blog. Pokémon Black and White were referred to as a “new generation of Pokémon”, and Pokémon Sun and Moon were referred to as the “newest generation” in press releases.
Generational lines are typically ignored in other parts of the franchise, which continue from where the last generation left off and keep the story going (this is especially true of the anime), and may ignore older parts of the canon that explicitly declare to be true something that is later changed.
To date, there are eight generations, each introducing their own quirks into the franchise. The Generation I and II games are compatible with one another via the Time Capsule but not with later games; the six most recent generations are also compatible with each other (forward only) via dual-slot mode, Pal Park, Poké Transfer, Poké Transporter, Pokémon Bank and Pokémon Home, but not with the Generation I and II games, with the exception of the Generation I and II Virtual Console releases, which are compatible with Generation VII.