Which Pokémon video games first introduced Pokémon breeding?

Pokémon Gold and Silver first introduced Pokémon breeding to the core video-game series.

Released for the Game Boy Color, the games added a Pokémon Daycare system in which compatible Pokémon could produce an Egg. The Egg could then hatch into a Pokémon, creating a new way to obtain species and pass down certain characteristics.

Breeding also supported the introduction of Baby Pokémon, including Pichu and Igglybuff. These younger forms were generally obtained by breeding their evolved relatives rather than finding them in the wild.

Pokémon Gold and Silver are sometimes confused with Pokémon Crystal because Crystal expanded and refined the second-generation experience. However, the breeding concept itself debuted with the paired Gold and Silver games. The same generation also introduced held items, Shiny Pokémon, and the Dark and Steel types.