Shield Charm

The Shield Charm is a term applied to several varieties of charms that create a magical barrier to deflect physical entities and spells. The latter may sometimes rebound directly off it back towards the caster and at others may ricochet off in other directions or dissipate as soon as they hit the shield. It will not repel any effectively cast Unforgivable Curse.

The Shield Charm is a moderately difficult spell. Fred and George Weasley realised that most adult wizards, even those employed by the Ministry of Magic, could not produce a functional Shield Charm. They used this to their advantage when marketing their line of protective clothing (hats, cloaks, etc), upon which Shield Charms were cast.

The incantation for the simplest Shield Charm spell is Protego. Incantations for other varieties of the Shield Charm include Protego Duo, Protego Horribilis, Protego Totalum and Protego Maxima.

Harry Potter

 * Harry Potter first learned this spell in his preparations for the Third Task of the Triwizard Tournament, during which his friends Ron Weasley and Hermione Granger shot spells at him so that he could practice shielding himself.
 * Harry once used the charm to defend himself against Professor Snape's Legilimency during Occlumency training, and found himself unexpectedly seeing some of Snape's memories. This eventually led to Snape using a Pensieve to store his memories.
 * Harry used the spell multiple times during the Battle of the Department of Mysteries in order to protect himself and his fellow D.A. members from Death Eaters, and to prevent them from summoning the prophecy away from him that night.
 * Harry cast the charm between Hermione and Ron after the latter returned, since Hermione was furious with Ron to the point of wanting to curse him.
 * Harry used the charm multiple times during the Battle of Hogwarts to protect various fighters on his side, such as Molly Weasley after she killed Bellatrix Lestrange.

Other

 * Gilderoy Lockhart presumably attempted to demonstrate this charm, or something similar, to Harry during the first meeting of his duelling club, but failed spectacularly, dropping his wand in the process.
 * This charm was among those that Harry taught the members of Dumbledore's Army in his fifth year.
 * In 1996, Dolores Umbridge used a shield charm to protect herself from the centaurs' arrows in the Forbidden Forest.
 * Hermione Granger managed to cast this nonverbally in their first sixth year Defence Against the Dark Arts lesson.
 * Remus Lupin, Nymphadora Tonks, and various other guests at Bill Weasley and Fleur Delacour's wedding in 1997 cast shield charms after Kingsley Shacklebolt's Patronus arrived to warn those at the Burrow that Lord Voldemort had taken over the Ministry of Magic.
 * Hermione Granger cast the Shield Charm in 1997 when Harry and Ron got into an argument during their search for the Horcruxes. Hermione cast the shield before they could draw their wands against one another. When Ron subsequently left, Hermione was hampered in trying to follow him and persuade him not to leave by her own shield.
 * Severus Snape cast this charm to deflect Harry Potter's spells during their brief duel after he killed Albus Dumbledore.
 * Severus later used the Shield Charm during his duel with Minerva McGonagall.

Known users

 * Dolores Umbridge
 * Dumbledore's Army
 * Harry Potter
 * Hermione Granger
 * Remus Lupin
 * Severus Snape
 * Bellatrix Lestrange
 * Kingsley Shacklebolt
 * Nymphadora Tonks

Etymology
Latin protego, "I cover" or "I protect".

Known Variations

 * Protego Duo
 * Protego Horribilis
 * Protego Maxima
 * Protego Totalum

Behind the scenes

 * In the films, it has been noticed that wizards/witches are able to parry spells as if their wand was a saber. This may be a non-verbal variant of the shield charm. Another possibility is that wands themselves have inherent magical qualities that allow some spells to be rebounded off of them.

Appearances

 * Harry Potter and the Goblet of Fire 
 * Harry Potter and the Order of the Phoenix
 * Harry Potter and the Order of the Phoenix (film)
 * Harry Potter and the Order of the Phoenix (video game)
 * Harry Potter and the Half-Blood Prince
 * Harry Potter and the Half-Blood Prince (film)
 * Harry Potter and the Half-Blood Prince (video game)
 * Harry Potter and the Deathly Hallows
 * Harry Potter and the Deathly Hallows Part 1
 * Harry Potter and the Deathly Hallows: Part 1 (video game)
 * Harry Potter and the Deathly Hallows Part 2
 * Harry Potter: Spells

Notes and references
Charme du Bouclier Kilpiloitsu