Fairies, particularly those of Irish, English, Scottish and Welsh folklore, have been classified in a variety of ways. Classifications – which most often come from scholarly analysis, and may not always accurately reflect local traditions – typically focus on behavior or physical characteristics.

Germanic lore featured light and dark elves (Ljósálfar and Dökkálfar). This may be roughly equivalent to later concepts such as the Seelie and Unseelie.

In the mid-thirteenth century, Thomas of Cantimpré classified fairies into neptuni of water, incubi who wandered the earth, dusii under the earth, and spiritualia nequitie in celestibus, who inhabit the air.

In 1566, John Walsh of Devonshire – on trial for witchcraft – said that there were three kinds of "feries": white, green and black.

The sidhe in celtic mythology are also known as fairies.

In Scottish folklore, faeries are divided into the Seelie Court and the Unseelie Court. D. L. Ashliman notes that this may be the most famous division of fairies.

The Seelie Court is described to comprise fairies that seek help from humans, warn those who have accidentally offended them, and return human kindness with favors of their own. Still, a fairy belonging to this court would avenge insults and could be prone to mischief.

The Unseelie Court describes the darkly-inclined fairies. Unlike the Seelie Court, no offense was deemed necessary to bring down their assaults. In Scotland, they were seen as closely allied with witches.