Egg Group

Egg Groups are divided into 21 categories that determine how Pokémon are able to interbreed. Similar to types, a Pokémon may belong to one or more Egg Groups. Egg Groups are based on biological traits of a Pokémon and often belong to the same evolutionary chain.

Egg Groups are often preserved along the same evolutionary chain. Such as Machop and its evolutions sharing the Humanoid Group. It can differ for some evolutionary chains such as Feebas classified to the Fish Group and its evolution Milotic classified to the Serpent Group. This allows for Pokémon to breed in unique movesets and special traits.

List of Egg Groups
This is a complete list of Egg Groups:
 * Monster Group
 * Aquatic Group
 * Plant Group
 * Insect Group
 * Bird Group
 * Beast Group
 * Rodent Group
 * Serpent Group
 * Pixie Group
 * Marine Group
 * Fish Group
 * Humanoid Group
 * Subaqueous Group
 * Mineral Group
 * Amorphous Group
 * Artifact Group
 * Primate Group
 * Livestock Group
 * Draconic Group
 * Universal Group
 * Undiscovered Group
 * Unknown Group

Trivia

 * PokéUniversity Scholar Eugene Nicks is credited with the discovery of Pokémon Egg Group categorization and environmental impacts on Pokémon breeding patterns.
 * Johtonian Professor Henry Elm specalizies in Pokémon breeding and is credited with the discovery of Pokémon Eggs.