Eevee evolves into Vaporeon when exposed to a Water Stone. The Water Stone is an evolution stone that triggers an immediate transformation, so Eevee does not need to gain a level or learn a particular move first.
Vaporeon is one of Eevee’s original three evolutionary forms, introduced in Pokémon Red and Blue. The other two are Jolteon, created with a Thunder Stone, and Flareon, created with a Fire Stone. Together, these three forms are often called the original Eeveelutions.
The evolution reflects Vaporeon’s aquatic design and Water typing. Vaporeon’s Pokédex descriptions often emphasize its ability to blend into water, while its body includes features such as fins and a mermaid-like tail. In battle, it is known for high HP and strong Special Attack, making it a durable Water-type choice in many games.
A common mix-up is assuming that all Eevee evolutions use stones. Later forms use other conditions: Espeon and Umbreon require high friendship at different times of day, while Leafeon and Glaceon have used location-based or item-based methods depending on the game.