Through Generation IX, Eevee has eight different evolutions, collectively called Eeveelutions. They are Vaporeon, Jolteon, Flareon, Espeon, Umbreon, Leafeon, Glaceon and Sylveon.
Eevee first appeared in Generation I with three possible evolutions: Vaporeon, Jolteon and Flareon. Generation II added Espeon and Umbreon, Generation IV added Leafeon and Glaceon, and Generation VI introduced Sylveon. No new Eeveelution was added in Generations VII, VIII or IX.
Eevee’s branching evolution methods include elemental stones, friendship, time of day, location-based effects and a move-related condition. Pikachu is not an Eeveelution, and Eevee itself is the unevolved species, so neither changes the count of eight.