Eevee has eight possible evolutionary forms. These forms are commonly called Eeveelutions and give Eevee the greatest number of distinct evolutions among Pokémon species.
The original three are Vaporeon, Jolteon, and Flareon, introduced with Pokémon Red and Green. Pokémon Gold and Silver added Espeon and Umbreon, while Pokémon Diamond and Pearl introduced Leafeon and Glaceon.
The eighth form, Sylveon, arrived in Pokémon X and Y with the Fairy type. Eevee itself is a Normal-type Pokémon whose unstable genetic structure allows different evolutionary outcomes depending on items, locations, friendship, or other game conditions.
The count is eight completed, officially released forms. A planned Flying-type Eeveelution was reportedly considered for Pokémon Sun and Moon but was not released, so it does not increase the total. Pikachu and Eevee are also mascots of separate Pokémon: Let’s Go games.