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. Conjurations may sometimes rebound directly off it back towards the caster, or, in other cases, may ricochet off in other directions or dissipate as soon as they hit the shield.

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 (something that Harry Potter was able to not only accomplish but also impart to members of the D.A.). They used this to their advantage when marketing their line of protective clothing (hats, cloaks, etc), upon which permanent 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 was most likely the reason why Snape was using a Pensieve to store his memories, and thus to preserve his privacy.
 * 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 from him that night.
 * During his first sixth year Defence lesson, Harry and the other members of his class had to cast this spell non-verbally. When Snape tried to jinx him, Harry instinctively used a Shield Charm (verbally cast) that was powerful enough to throw Snape off his feet.
 * 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

 * In 1484, Hannah Cockleford used the Shield Charm to protect a Muggle boy named Edmund Gaddlegate when he was forced to joust with the Earl of Paunchley.
 * Gilderoy Lockhart presumably attempted to demonstrate this charm, or something similar, to Harry during the first meeting of his duelling club, but all he truly wanted was to twirl his wand fancifully, which 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.
 * During the Battle of the Department of Mysteries, the fighting Death Eaters cast many Shield Charms to protect themselves from Dumbledore's Army's Stunning spells.
 * 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.
 * Lord Voldemort used a Shield Charm to defend himself during his duel with Albus Dumbledore.
 * Voldemort also used many Shield Charms when duelling Harry Potter and many others during the Battle of Hogwarts.

Known users

 * Dolores Umbridge
 * Dumbledore's Army
 * Harry Potter
 * Hermione Granger
 * Sirius Black
 * Remus Lupin
 * Severus Snape
 * Bellatrix Lestrange
 * Kingsley Shacklebolt
 * Nymphadora Tonks
 * Lucius Malfoy
 * Lord Voldemort
 * Ginny Weasley

Known Variations

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

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

Behind the scenes

 * In the films, Shield Charms are used in nearly every duel shown, almost always used non-verbally and usually accompanied by a parry-like wand movement.
 * In the early video games, Expelliarmus functions as a shield charm, due to a lack of enemies to Disarm. In these games, Protego is absent.
 * In Harry Potter and the Deathly Hallows: Part 2, Protego is shown several times to be able to block the Killing Curse. According to the books this is incorrect as the Killing Curse is "unblockable" which is the main reason for its particular infamy, but within the context of the films the fact is never mentioned.

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 and the Deathly Hallows: Part 2 (video game)
 * LEGO Harry Potter: Years 5-7
 * Harry Potter: Spells
 * Pottermore
 * Wonderbook: Book of Spells