Shield Charm

The Shield Charm is a charm that creates an magical barrier which deflects minor to moderate hexes as well as physical objects. Spells will sometimes rebound off it directly back towards their caster. Other times they will ricochet off in other directions or dissipate as soon as they hit the shield, or around the caster's sides. It will not repel any effectively cast Unforgivable Curse. The incantation for this spell is Protego.

The Shield Charm is a moderately difficult spell. Fred and George Weasley realized 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.

In the films, it has been noticed that wizards/witches are able to parry spells as if their wand was a saber. It could be that they are skilled enough to reduce the size of the charm to cover the small area around the wand or that the wand itself can be used sometimes to block smaller spells.

The Shield Charm has several variants, such as the Protego Duo, Protego Horribilis, and Protego Totalum.

Known uses

 * 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.
 * This charm was among those that Harry taught the members of Dumbledore's Army in his fifth year.
 * 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.
 * In 1996, Dolores Umbridge used a shield charm to protect herself from the centaurs' arrows in the Forbidden Forest.
 * 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.
 * 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.
 * 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.
 * Severus Snape cast this charm during his duel with Minerva McGonagall.
 * Harry used the charm multiple times during the Battle of Hogwarts to protect various fighters on his side, such as Molly Weasley.

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 I (video game)

Notes and references
Charme du Bouclier Kilpiloitsu