"Expelliarmus is a useful spell, Harry, but the Death Eaters seem to think it is your signature move, and I urge you not to let it become so!”
“I won’t blast people out of my way just because they’re there ... That’s Voldemort’s job.”
-- Remus Lupin and Harry Potter (DH5)
Causes opponent’s weapon to fly out of his or her hand. The opponent is then said to have been Disarmed.
References from the canon
- Basic defensive spell, taught at the Duelling Club by Snape (CS10) used frequently thereafter. If the exact nature of the opponent's weapon is uncertain, the spell can have unexpected results. If several people cast the spell simultaneously, the target may be rendered unconscious (PA19, GF31, GF34)
- Lupin used this on Harry, Ron, and Hermione simultaneously in the Shrieking Shack on the night they first met Sirius Black (PA17).
- Snape's use of this spell against Lockhart had rather violent results (CS10).
- When Harry faced Voldemort in the Little Hangleton Graveyard, the only duelling spell he knew was the Disarming Charm. When he attempted it, the Priori Incantatum, or "Reverse-Wand Effect" happened due to the fact that both his holly wand and Voldemort's yew wand contained "twin-wandcores" of Phoenix feather (GF34)
- This was the first spell taught at the first D.A. meeting. Zacharias Smith thought this was silly, but Harry pointed out that he used that spell against Voldemort just a few months before and that it had saved his life (OP18).
- Harry cast this at Stan Shunpike during the Battle of the Seven Potters (DH4).
- Used by Ron against Bellatrix Lestrange at Malfoy Manor (DH23).
- Harry again used this against Voldemort during their final duel (DH36).
- Referred to in verb form Disarm (DH4, DH5, etc.)
- When Harry and Draco argued and duelled at the Ministry nineteen years after the Battle of Hogwarts, they tried the Disarming Charm simultaneously and each wand repelled the other but did not fly out of their hands (CC2.13).
- Voldemort's daughter Delphi practices "Expelliarmus" with Albus Potter in the Forbidden Forest, during which she jokes that he is a "positively disarming young man" (CC2.4).
- Albus later uses the charm on Cedric Diggory in an alternate universe to take his wand and make him lose the First Task of the Triwizard Tournament in an attempt to change events and keep him from dying in the graveyard with Voldemort (CC2.7).
- Scorpius Malfoy discusses with Professor Snape, Hermione Granger and Ron Weasley what spells he and Albus Potter had used to change time - so that they can be reversed, one being the Disarming Charm (CC3.7, CC3.8).
- In another timeline during the Third Task, Delphi is disarmed by Cedric in the Maze as she tried to use the Cruciatus Curse on Albus and Scorpius Malfoy, who were trying to make sure Cedric went to his fate so the future would stay the same (CC3.20).
"expelo" L. to drive out + "arma" L. weapon
During the Battle of the Seven Potters, Harry used "Expelliarmus" several times, but Lupin later chastised him for not using his "signature spell" instead of something more powerful. But each time Harry made the hero's choice to disarm instead of maim or kill, things worked out for him.