Eevee has eight different evolutions in the main Pokémon series. These forms are commonly called Eeveelutions and cover several elemental types introduced across generations.
The eight are Vaporeon, Jolteon, Flareon, Espeon, Umbreon, Leafeon, Glaceon and Sylveon. The first three appeared in the original games, while the others were added in later generations as new evolution methods and types became available.
Eevee’s unusual biology allows it to evolve through different conditions rather than following one fixed path. Evolution stones create Vaporeon, Jolteon and Flareon; friendship and time of day produce Espeon or Umbreon; location or specific items historically produced Leafeon and Glaceon; and friendship plus a Fairy-type move leads to Sylveon.
Eevee itself does not count as an evolution. Pikachu and Raichu are also not Eeveelutions, despite being familiar branching species. The number eight reflects the main-series forms available through Generation IX.