In Norse mythology, the Svartálfar ("black elves") or Dökkálfar ("Dark elves") are supernatural beings that are said to reside in the underground world of Svartálfaheim. They, like the trolls, are often correlated with the dvergar ("dwarves") and their home is often considered to be the same as Niðavellir, an underground area beneath Midgard.
Svartálfar derives from Old Norse "vættir" meaning wights. Svartálfar acquired their name because they were seen as the light-avoiding counterparts to the common elf, living in Álfheim. Snorri Sturluson, author of among other things the Prose Edda, at times refer to the light elves as Ljósálfar. The term black or dark elf might rather be suggestive of their place of residence than of their presumed nature.
Svartálfar are described as human-like, but ugly and misshapen.
The Svartálfar are often identified with the dvergar (dwarfs) and are hard to distinguish from the Döckálfar (the earth-dwelling ones).
Kevin Crossley-Holland states that:
"No valid distinction though can be drawn between the dwarfs and the dark elves; they appear to have been interchangeable." Confusion between unrelated, mythologic entities does arise over time, for example in the stories of the trolls (ogre-like beings that are also confused with dwarves).
Svartálfar are described as greedy and troublesome for humans. In a similar fashion to the Scandinanvian Mara and German Albtraum, dark elves will sit upon the dreamer's chest and/or whisper the bad dreams into the sleeper's ears.
Besides their underground lives, Svartálfar had many of the same traits attributed to them as the dwarves. These include growing from the maggots of Ymir's flesh or turning to stone when exposed to daylight.