House-elves are small elves that are used by wizards as slaves. They are loosely based on the Hiberno-British mythological brownie or hobgoblin. They are 2–3 feet tall, with spindly arms and legs 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 and use a strange manner of speaking. House-elves are generally obedient, pliant, and obsequious. Rather than conventional clothing, house-elves 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 their own forms of powerful 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, in a manner similar to Apparition; they are able to do this even within the boundaries of Hogwarts and other places where Anti-Apparition and Anti-Disapparition charms are in effect, preventing human Apparition and Disapparition. House-elves can, however, use side-along Apparition to transport humans. The full nature of the elves' magic is never fully disclosed, but it seems to be quite 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. In Harry Potter and the Goblet of Fire, when 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". Later, 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' non-wand magic.
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".
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 his former masters even after freed. However, he is able to overcome it more as time passes, even going so far as to defiantly tell Bellatrix Lestrange that none of the Malfoys is masters over him. According to Kreacher, "a House-elf's highest law is his master's bidding"; however, while House-elves must obey their masters whatever their personal feelings may be, they are far from mindless automata. House-elves have been known to disobey the rules (usually by finding, when necessary, 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 of bullying and mistreating House-elves; the Malfoys forced Dobby to slam his own ears in the oven door or iron his hands if he attempted to disobey them; the Black family had a tradition of decapitating House-elves who were too old to carry a tea tray, then placing their stuffed and mounted heads on a wall.
Most House-elves would be devastated if freed, for it would mean that they had failed to serve their masters properly; but Dobby enjoys being free. Though he summons the courage to request payment when he is hired at Hogwarts, even Dobby does not want to be paid too much. Most people in the wizarding community are unwilling to pay a House-elf, as this would obviate the point of having one. Indeed, most House-elves seem to regard paid service as a disgrace to their species. During her time at Hogwarts, Hermione Granger establishes S.P.E.W (the Society for the Promotion of Elfish Welfare) to champion House-elf's rights, a movement that garnered little interest from her classmates or from 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 the house elf, confides in Harry that the other House-elves find the idea so insulting that Dobby is the only resident elf still willing to clean in Gryffindor Tower. According to Rowling, Hermione works in the Ministry of Magic after Hogwarts and manages to make positive changes for House-elf rights.