"House-elves is not supposed to have fun, Harry Potter. House-elves does what they is told."
     -- Winky the House-Elf

House-elves are small humanoid creatures who inhabit large houses belonging to wealthy Wizarding families. They are "bound" to the family of the house, which means they do all manner of menial tasks for them until they die. House-elves are apparently very happy with this arrangement and consider it a matter of pride that they serve faithfully and do not betray their families. 

There are over a hundred house-elves at Hogwarts; there they lay the fires, do the laundry, light the lamps, and do countless other such tasks. The House-Elves are also the chefs of the castle and they create wonderful meals in the huge kitchens.

A house-elf is a short creature with large bat-like ears and enormous eyes. It is difficult to tell the difference between male and female house-elves, although the female generally has a higher, squeakier voice (GF8). Both male and female house-elves do not wear clothing (and would consider it shameful to do so) but cover themselves in towels, tea cozies, or pillowcases. If their owner gives them an article of clothing, it breaks the "enslavement" and the house-elf is free. For most house-elves, this would be the ultimate insult and they would be shamed forever.

However, a house-elf named Dobby, who served the Malfoy family, took a more enlightened view. He desperately wanted to be free and eventually Harry Potter managed to trick Lucius Malfoy into giving Dobby an old sock. Dobby has since come to work at Hogwarts, where he actually receives payment for his labors. 

Dobby has huge, green, tennis ball-sized eyes and a long thin nose like a pencil. He is quite short, like all House-Elves, coming only up to Harry's navel (GF21). He is devoted to Harry Potter and also to Ron Weasley, who he refers to as Harry's "Wheezy." Dobby is particularly fond of socks and has begun using his earnings to buy yarn and knit them himself. 

Winky, a female house-elf who until recently worked for the Crouch family, has enormous brown eyes and a nose like a tomato. She has also come to work at Hogwarts, but she is in total disgrace and has taken to sitting on a stool by the fireplace and getting drunk on butterbeer. For years, Winky took care of Barty Crouch Jr., who was held in the Crouch residence under the Imperius Curse. Barty Crouch Sr. fired her when she was found holding a wand at the Quidditch World Cup. Winky's mother and grandmother were also Crouch family House-Elves (GF21)

House-elves have a very powerful magic all their own, magic which requires none of the types of focusing tools (wands or words) that Wizard magic requires. Dobby used his magic to enchant a Bludger, to close the magic portal that leads to Platform Nine-and-Three-Quarters, to interfere with Owl Post and steal someone's letters, and to knock Lucius Malfoy down a flight of stairs. He also can disappear at will, which would seem to be a form of Apparition, but a form which can be done within Hogwarts, where, as Hermione constantly reminds Harry and Ron, normal Wizarding Apparition is simply not possible. All of these are very powerful charms.

Unfortunately, as long as they're enslaved, they aren't likely to be using this magic for anything but their mundane work. Hermione Granger is working to bring enlightened thinking to the house-elves at Hogwarts, so far with very little success. It would be interesting indeed if she would succeed in convincing these creatures to stand up for themselves and perhaps even fight against Voldemort.