The Department for the Regulation and Control of Magical Creatures of the Ministry of Magic is responsible for overseeing and regulating magical creatures. It is divided into three divisions: the Beast Division, the Being Division, and the Spirit Division. A "being" is generally defined, according to Fantastic Beasts, as "any creature that has sufficient intelligence to understand the laws of the magical community and to bear part of the responsibility in shaping those laws." This includes humans, goblins, hags, and vampires. In accordance with this definition, fairies, pixies, gnomes, and most other creatures are classified as "beasts". Centaurs and merpeople are said to have rejected "being" status in favour of "beast" status, as have leprechauns. Werewolves and Animagi are notable because they are typically in human form — a werewolf transforms from human state only at the full moon, and an Animagus is a human who has learned to transform into an animal at will. Their classification is unclear, and offices responsible for werewolves exist in both the Beast and Being Divisions. Affairs related to ghosts come under the auspices of the Spirit Division.
The Department for the Regulation and Control of Magical Creatures classifies magical creatures on a scale from X to XXXXX as follows:

X: Boring
XX: Harmless / may be domesticated
XXX: Competent wizards should cope
XXXX:Dangerous / requires specialist knowledge / skilled wizard may handle / must be respected
XXXXX:Known wizard killer / impossible to train or domesticate