Vampires
Werewolves
Mages
The Created
The Fae
The Bound
The Hunters

The Physical Realm
The physical world is the world that humanity inhabits, identical to our own. Events that occur in the Physical Realm affect those in the other two. The Shadow Realm births new spirits to represent the physical objects and new ideas that are created in the material plane.
The Twilight Realm
Not truly a realm in and of itself, the Twilight is simply the world of invisible beings on the physical plane. When something is referred to as being "in twilight" it means it is just one step in and out of the Physical and Shadow realms. Ghosts and Spirits in the Physical Realm are always considered to be in the Twilight until they fully manifest themselves in a material form. Also, Ghosts only exist in Twilight, they cannot cross into the Shadow completely.
The Shadow Realm
Acting as a dark mirror to the physical world, the Shadow is where Spirits of all kinds dwell and are born.
Werewolves and those Mages who have knowledge of the Spirit Arcanum can move freely into the Shadow realm and manipulate Essence, the energy that makes up Spiritual matter. With this they can communicate with, learn from, and command Spirits.