Which Pokémon generation introduced breeding between compatible Pokémon?

Generation II introduced Pokémon breeding between compatible Pokémon.

The mechanic debuted in Pokémon Gold and Silver, released in Japan in 1999. Players could leave compatible Pokémon at the Pokémon Day Care and later receive an Egg. After walking a required distance, the Egg hatches into a Pokémon, often inheriting characteristics from its parents.

Breeding added a new layer to team building and collection. It allowed players to obtain baby Pokémon, pass down certain moves, and pursue specific combinations of traits. The system also introduced the idea that some species appear as Eggs rather than being found directly in the wild.

Breeding is not the same as Pokémon evolution. A bred Pokémon begins as an Egg and usually hatches into a young Pokémon, while evolution changes an existing Pokémon after conditions such as leveling up, using an item, or reaching a friendship threshold. The original Gold and Silver games also introduced 100 new species, bringing the Pokédex total from 151 to 251.