By the end of Generation VI, Eevee had eight different evolutions.
These forms are Vaporeon, Jolteon, Flareon, Espeon, Umbreon, Leafeon, Glaceon, and Sylveon. Because each evolution uses a different method or condition, Eevee became one of the franchise’s most recognizable examples of branching evolution.
The first three evolutions appeared in the original games and represent Water, Electric, and Fire. Espeon and Umbreon arrived in Generation II, while Leafeon and Glaceon were added in Generation IV. Sylveon completed the Generation VI set.
Eevee’s number of evolutions is often misstated because the total can change when later games introduce new forms. The figure here is specifically tied to the end of Generation VI.