Those professions who combine two realms of magic to interact with the world in their own way.  There are three categories of hybrid casters.

Essence and Channeling:
Sorcerer: Those whose magic targets the destruction of both animate and inanimate matter (CL page 24)
Summoner: Those who deal with the communication and summoning of creatures (ChComp page 23)

Essence and Mentalism:
Mystic: Those who use magic to influence the mind with misdirection and modification (CL page 23)

Channeling and Mentalism:
Healer: Those who take injuries upon themselves to heal with their impressive recuperative powers (CL page 22)
Warlock: Those who manipulate people and their fate in a number of ways (ChComp page 24)