Imp - a creature native to Britain and Ireland. It isn't a pixie, though both are six to eight inches in height. Colored dark brown to black, imps prefer to live in marshy conditions and are frequently found near river banks. They get amusement from pushing and tripping the unwary.

Impedimenta (Spell) - to slow down the one pursuing you.

Imperious Curse (Spell) - the first of the three Unforgivable Curses. This one allows the wizard to gain complete control over the actions of another.

Imperturbable Charm (Spell) - magic which creates a barrier on an object. The easiest way to test for this charm is to throw an item (which bounces off the "imperturbed" thing without ever touching it) in its direction.

Impervius (Spell) - a spell to waterproof something.

Incarcerous (Spell) - a spell that creates ropes which bind someone.

Incendio (Spell) - the fire-starting spell.

Inferius (plural: inferi) - "inferi" is Latin for "the dead". They are corpses animated by a Dark Wizard/Witch to do his/her bidding.

Instant Scalping (Spell) - instantly removes hair.

Invisibility Cloak - this magical item is rare, though not too unusual, as Ron Weasley recognized it for what it is. Harry inherited the cloak from his father via Dumbledore, and he certainly found his own uses for it, much the same way that mythological and fictional characters have found uses for other artifacts that confer invisibility upon its wearer. See Demiguise.

Hades (meaning "the unseen one" in ancient Greek), the Greek god of the underworld, owned a "cap of darkness" that made one unseen. There were other items in Greek legend which gave the gift of being invisible, such as rings, arrows and even clouds of mist, but it wasn't until the Middle Ages that an actual cloak was said to bestow invisibility upon one. "The Song of the Nibelung" was a twelfth-century Austrian poem, in which a powerful dwarf magician named Alberich owns such a cloak. This cloak also gives its wearer the strength of twelve men. Alberich uses his magical garment to protect the underground treasure of the Nibelung (a race of European kings), until the German folk hero, Siegfried, defeats him and takes the cloak for himself. Nineteenth-century German composer Richard Wagner based his opera, "Der Ring des Nibelungen", upon this story.

In addition to being strong twelve times over, some cloaks possessed powers such as the ability to fly. One like this appeared in a sequel to "The Wizard of Oz."