Which Pokémon games first introduced breeding through Eggs?

Pokémon Gold and Silver first introduced breeding through Eggs.

In these Game Boy Color games, compatible Pokémon left at the Pokémon Day Care could produce an Egg. The Egg could then be carried by the player until it hatched, adding a new way to obtain and raise Pokémon. The offspring generally belongs to the mother’s species, while some inherited moves can come from the father.

Breeding added strategic depth beyond catching wild Pokémon. Players could produce young Pokémon with particular moves, abilities in later games, or desirable statistics. Ditto also became especially useful because it can breed with most Pokémon outside the No Eggs Discovered group.

Not every Pokémon can breed. Legendary and Mythical Pokémon are generally excluded, and compatibility depends on breeding groups. The mechanic is sometimes confused with Pokémon Day Care itself, which existed for raising Pokémon before Gold and Silver; breeding is the feature that these games introduced.