There are three major (and numerous minor) Inquisitorial branches or orders that focus on specific types of threats and train "specialist" Inquisitors. Joining one of the orders is common, but not mandatory. The major orders are:
- Ordo Xenos: Investigates and eliminates alien influence and plots against the Imperium.
- Ordo Malleus: Destroys daemonic threats and investigates their nature.
- Ordo Hereticus: Investigates heresy, mutation, and rogue psykers; also polices the Ecclesiarchy.
Each of the Orders has a Chamber Militant, an attached military unit. Ordo Xenos has the Deathwatch, an assemblage of veteran Space Marines; Ordo Malleus has an entire Marine Chapter, the Grey Knights, an elite all-psyker force that hurts daemons by their sheer presence; Ordo Hereticus has the Adeptas Sororitas, an all-female force.