Which three Eeveelutions debuted alongside Eevee in Pokémon Red and Blue?

Vaporeon, Jolteon, and Flareon debuted alongside Eevee in Pokémon Red and Blue.

Eevee is known for its unstable genetic code, which lets it evolve into Pokémon with different types. In the original games, a Water Stone produced Vaporeon, a Thunder Stone produced Jolteon, and a Fire Stone produced Flareon.

Five additional Eeveelutions were introduced in later generations: Espeon and Umbreon in Gold and Silver, Leafeon and Glaceon in Diamond and Pearl, and Sylveon in X and Y. This brought the total number of official Eeveelutions to eight.

The three original forms are sometimes grouped as the first-generation Eeveelutions. They should not be confused with the later forms, which use friendship, location, learned moves, or other evolution conditions.