Evasion

Evasion helps Trainers and Pokémon avoid attacks. There are three types of Evasion: Physical Evasion, Special Evasion, and Speed Evasion. To calculate these Evasion values, divide the related Combat Stat by 5 and round down. You may never have more than +6 in a given Evasion from Combat Stats alone.
For every 5 points a Pokémon or Trainer has in Defense, they gain +1 Physical Evasion, up to a maximum of +6 at 30 Defense. Physical Evasion from Defense applies to all Physical attacks.
For every 5 points a Pokémon or Trainer has in Special Defense, they gain +1 Special Evasion, up to a maximum of +6 at 30 Special Defense. Special Evasion from Special Defense applies to all Special Attacks.
For every 5 points a Pokémon or Trainer has in Speed, they gain +1 Speed Evasion, up to a maximum of +6 at 30 Speed. Speed Evasion from Speed applies to all attacks. This includes Physical, Special, and Status Attacks.
Evasion from Stats (Defense, Special Defense, Speed, and Combat Stages) caps at -6/+6 per Evasion type.
Evasion from non-Stat sources (Features, Training, Items, Statuses, Flanking) also caps at -6/+6 and stacks with Stat Evasion.
Because Accuracy Checks cannot be modified by more than +9, total effective Evasion caps at +9. You cannot apply more than +9 Evasion at a time.
Changes to Evasion do not count as Combat Stages, but are cleared by any effects which reset Combat Stages.
Note that Flanking provides a -2 to Evasion and not a +2 to Accuracy.