House-elves are small elves used by wizards as slaves. They are 2–3 feet tall, with spindly limbs and oversized heads and eyes. They have pointed, bat-like ears and high, squeaky voices. Their names are usually pet-like diminutives, and do not appear to have surnames. They habitually refer to themselves in the third person. House-elves are generally obedient, pliant, and obsequious; and when enslaved, wear discarded items like pillowcases and tea-towels. House-elves' masters can free them by giving them an item of clothing, much like the Hob of English Folklore. House-elves can become intoxicated by drinking Butterbeer.
House-elves possess magic distinct from that used by wizards and witches, which they generally use in the service of their masters. This magic can be used without the permission of their masters, or even against their orders, though such disobedience obliges them to punish themselves in various painful ways. Among other things, this magic allows house-elves to travel instantly from place to place, even at Hogwarts and other places where human teleportation is prevented; and even to thus transport humans. The full extent of the elves' magic is never fully disclosed, but it seems formidable. Along with the ability to Apparate anywhere at any time, Dobby, Winky, Hokey, and Kreacher all demonstrate that they can overpower wizards when necessary: In Chamber of Secrets, Dobby forcefully repels Lucius Malfoy while protecting Harry Potter; whereas in Harry Potter and the Goblet of Fire, when the younger Barty Crouch is unmasked and confesses to what happened on the night of the Quiddich World Championship, he says: "Winky used her own brand of magic to bind me to her", and in Deathly Hallows, Kreacher is ordered by Harry to capture Mundungus Fletcher and bring him to 12 Grimmauld Place, a task that he accomplishes within a few days;–– even though, as Kreacher puts it, "He has many hidey-holes and accomplices". Moreover, although House-elves are not allowed to carry wands, the magic they can perform without wands is considerably greater than that of wizards' magic.
In Goblet of Fire, it is said that a House-elf who has been freed is normally told to find a new family to serve. There is an Office of House-Elf Relocation at the Ministry of Magic. House-elves are unendingly loyal to their human families; so much so, that Dobby, who served the Malfoy family, attempts to punish himself each time he utters a negative remark about them (even after his freedom) until the final book, in which he defies Bellatrix Lestrange. According to Kreacher, "a House-elf's highest law is his master's bidding"; however, while House-elves must obey their masters without question, they have been known to disobey the rules (usually by finding loopholes in orders that allow for unintended interpretations) to protect themselves or their friends. Because of their docile, obedient natures, some families abuse their house-elves; Dark wizard families in particular seem to make a habit thereof, as when the Malfoys forced Dobby to torture himself, or when the Black family customarily decapitated their house-elves as they became enfeebled by age. Nonetheless, most house-elves are horrified by freedom even from the most cruel masters. Dobby, the first introduced, is the sole exception; but this extends chiefly to voluntary service, paid labour, and choice of his own employment and costume. During her time at Hogwarts, Hermione Granger establishes S.P.E.W (the 'Society for the Promotion of Elfish Welfare') to champion House-elve's rights; but gained little interest from her classmates or House-elves. After Hermione begins leaving elf-sized clothes around the Gryffindor common room, intending for Hogwarts' House-elves to inadvertently free themselves while cleaning, Dobby confides in Harry that the other House-elves find the idea so insulting that Dobby is the only resident elf willing to clean in Gryffindor Tower. According to Rowling, Hermione works in the Ministry of Magic after Hogwarts and thus increases House-elf rights; but this is never seen in the books, wherein their last appearance is at the Battle of Hogwarts, led by Kreacher against the antagonists.
In Deathly Hallows, Dumbledore tells Harry: "Of House-elves (...) Voldemort knows and understands nothing. Nothing. That they have a power beyond his own, a power beyond the reach of any magic, is a truth he had never grasped".