There are numerous monsters all over the world of Vana'diel. The vast majority of monsters belong to a certain Family of monsters. A family of monsters will generally possess similar traits and skills. For example, both the Beach Bunny and Variable Hare belong to the Rabbit Family and will typically possess the same abilities (e.g. Double Attack) and special attacks (e.g. Foot Kick). In addition, monsters from within a family will generally share certain behaviors and weaknesses (see Monster Classification).

Each family also has a Type, which generally describes a broad class of monster. Thus, the Rabbit Family is of the Beasts type. Monsters of one type may possess certain advantages or disadvantages when interacting with monsters of another type. To see how types interact with one another, see Ecosystems.

Certain rare and notorious monsters also inhabit the world of Vana'diel, and, if defeated, may reward the adventurer with rare and exclusive items and gil, in many cases.