Which Pokémon game was the first to introduce breeding and Pokémon Eggs?

Pokémon Gold and Silver were the first Pokémon games to introduce breeding and Pokémon Eggs.

The Generation II games added the Pokémon Day Care as a place where compatible Pokémon could produce an Egg. After an Egg is obtained, the player can carry it while walking until it hatches into a Pokémon. The system added a new way to obtain Pokémon and made inherited moves and traits important to experienced players.

Gold and Silver launched in Japan in 1999 and internationally in 2000. Along with breeding, they introduced 100 new species, held items, a day-and-night cycle, and the Dark and Steel types.

Pokémon Crystal is sometimes given as the answer because it is the enhanced version of Gold and Silver and is strongly associated with Generation II. However, breeding and Eggs were already present in the original Gold and Silver releases, so Crystal was not the feature’s debut.