Happiness is a feature that allows certain Pokémon to evolve.
While there is no way to track the exact happiness points of the Pokémon players are training, players can see that hearts will start to appear in the Pokémon's information. To see any Pokémon's information, players have to click its name to open the Pokédex. Hearts will appear as a Pokémon's happiness level is raised. The happiness will rise displaying one of four hearts: 
- A Pokémon needs 73 points to gain a heart. The exception is the last heart, which only takes 35 points.
- All Pokémon that need happiness hearts to evolve need 3 hearts (220 points). The exception is Sylveon, which needs 4 hearts (255 points). Sylveon is the final evolved form of Eevee.
- Since happiness points per battle is randomized (1 or 2), players would need somewhere between 37 to 73 battles in order to gain 1 heart for their Pokémon.
- Happiness is not reset when a Pokémon is traded.
Pokemon that evolve with Happiness
| Base Form | Required Happiness | Evolved Form |
 Golbat |
Level 3 Happiness |
 Crobat |
 Golbat (Halloween) |
Level 3 Happiness |
 Crobat (Halloween) |
| Golbat (Halloween) evolution is only available during certain events. | ||
 Meowth (Alolan) |
Level 3 Happiness |
 Persian (Alolan) |
 Chansey |
Level 3 Happiness |
 Blissey |
 Eevee |
Level 3 Happiness |
 Umbreon |
 Eevee (Christmas) |
Level 3 Happiness |
 Umbreon (Christmas) |
| Umbreon (Christmas) evolution is only available during certain events. | ||
| Eevee |
Level 3 Happiness |
 Espeon |
| Eevee (Christmas) |
Level 3 Happiness |
 Espeon (Christmas) |
| Espeon (Christmas) evolution is only available during certain events. | ||
| Eevee |
Level 4 Happiness |
 Sylveon |
 Pichu |
Level 3 Happiness |
 Pikachu |
 Pichu (Christmas) |
Level 3 Happiness |
 Pikachu (Christmas) |
| Pichu (Christmas) evolution is only available during certain events. | ||
 Pichu (Halloween) |
Level 3 Happiness |
 Pikachu (Halloween) |
| Pichu (Halloween) evolution is only available during certain events. | ||
 Cleffa |
Level 3 Happiness |
 Clefairy |
 Igglybuff |
Level 3 Happiness |
 Jigglypuff |
 Togepi |
Level 3 Happiness |
 Togetic |
 Togepi (Halloween) |
Level 3 Happiness |
 Togetic (Halloween) |
| Togepi (Halloween) evolution is only available during certain events. | ||
 Azurill |
Level 3 Happiness |
 Marill |
 Budew |
Level 3 Happiness |
 Roselia |
 Buneary |
Level 3 Happiness |
 Lopunny |
 Chingling |
Level 3 Happiness |
 Chimecho |
 Munchlax |
Level 3 Happiness |
 Snorlax |
 Riolu |
Level 3 Happiness |
 Lucario |
 Woobat |
Level 3 Happiness |
 Swoobat |
 Swadloon |
Level 3 Happiness |
 Leavanny |
 Frogadier |
Level 4 Happiness |
 Greninja (Ash) |
| Frogadier evolution is only available during certain events. | ||
 Type-Null |
Level 3 Happiness |
 Silvally |
 Snom |
Level 3 Happiness |
 Frosmoth |