John Duncan (painter) in the context of "Brigid of Kildare"

Aos sí (pronounced [iːsˠ ˈʃiː]; English approximation: /iːs ˈʃiː/ eess SHEE; older form: aes sídhe [eːsˠ ˈʃiːə]) is the Irish name for a supernatural race in Gaelic folklore, similar to elves. They are said to descend from the Tuatha Dé Danann or the gods of Irish mythology.

The name aos sí means "folk of the sí"; these are the burial mounds in which they are said to dwell, which are seen as portals to an Otherworld. Such abodes are referred to in English as 'shee', 'fairy mounds', 'elf mounds' or 'hollow hills'. The aos sí interact with humans and the human world. They are variously said to be the ancestors, the spirits of nature, or goddesses and gods.

Irish mythology is the body of myths indigenous to the island of Ireland. It was originally passed down orally in the prehistoric era. In the early medieval era, myths were written down by Christian scribes, who Christianized them to some extent. Irish mythology is the best-preserved branch of Celtic mythology.

The myths are conventionally grouped into 'cycles'. The Mythological Cycle consists of tales and poems about the god-like Tuatha Dé Danann, who are based on Ireland's pagan deities, and other mythical races like the Fomorians. Important works in the cycle are the Lebor Gabála Érenn ("Book of Invasions"), a legendary history of Ireland, the Cath Maige Tuired ("Battle of Moytura"), and the Aided Chlainne Lir ("Children of Lir"). The Ulster Cycle consists of heroic legends relating to the Ulaid, the most important of which is the epic Táin Bó Cúailnge ("Cattle Raid of Cooley"). The Fenian Cycle focuses on the exploits of the mythical hero Finn and his warrior band the Fianna, including the lengthy Acallam na Senórach ("Tales of the Elders"). The Cycles of the Kings comprises legends about historical and semi-historical kings of Ireland (such as Buile Shuibhne, "The Madness of King Sweeny"), and tales about the origins of dynasties and peoples.

The Tuatha Dé Danann (Irish: [ˈt̪ˠuə(hə) dʲeː ˈd̪ˠan̪ˠən̪ˠ], usually translated "folk of the goddess Danu"), also known by the earlier name Tuath Dé ("tribe of the gods" or "divine tribe"), are a supernatural race in Irish mythology. Many of them are thought to represent deities of pre-Christian Gaelic Ireland.

The Tuath Dé Danann are often depicted as kings, queens, druids, bards, warriors, heroes, healers and craftsmen who have supernatural powers. They dwell in the Otherworld but interact with humans and the human world. They are associated with the sídhe: prominent ancient burial mounds such as Brú na Bóinne, which are entrances to Otherworld realms. Their traditional rivals are the Fomorians (Fomoire), who might represent the destructive powers of nature, and whom the Tuatha Dé Danann defeat in the Battle of Mag Tuired. Prominent members include the Dagda ("the great god"); The Morrígan ("the great queen" or "phantom queen"); Lugh; Nuada; Aengus; Brigid; Manannán; Dian Cecht the healer; and Goibniu the smith, one of the Trí Dé Dána ("three gods of craft"). Several of the Tuath Dé are cognate with ancient Celtic deities: Lugh with Lugus, Brigit with Brigantia, Nuada with Nodons, Ogma with Ogmios, and Goibniu with Gobannus.

The aos sí (pronounced [iːsˠ ˈʃiː]; English approximation: /iːs ˈʃiː/ eess SHEE; older form: aes sídhe, áes sídhe [eːsˠ ˈʃiːə]) is a supernatural race in Irish folklore, similar to elves. They are said to descend from the Tuatha Dé Danann or the gods of Irish mythology.

The name aos sí means "folk of the sí"; these are the burial mounds in which they are said to dwell, which are seen as portals to an Otherworld. Such abodes are referred to in English as 'shee', 'fairy mounds', 'elf mounds' or 'hollow hills'. The aos sí interact with humans and the human world. They are variously said to be the ancestors, the spirits of nature, or goddesses and gods.

The Mythological Cycle is a conventional grouping within Irish mythology. It consists of tales and poems about the god-like Tuatha Dé Danann, who are based on Ireland's pagan deities, and other mythical races such as the Fomorians and the Fir Bolg. It is one of the four main story 'cycles' of early Irish myth and legend, along with the Ulster Cycle, the Fianna Cycle and the Cycles of the Kings. The name "Mythological Cycle" seems to have gained currency with Arbois de Jubainville c. 1881–1883. James MacKillop says the term is now "somewhat awkward", and John T. Koch notes it is "potentially misleading, in that the narratives in question represent only a small part of extant Irish mythology". He prefers T Ó Cathasaigh's name, Cycle of the Gods. Important works in the cycle are the Lebor Gabála Érenn ("Book of Invasions"), the Cath Maige Tuired ("Battle of Moytura"), the Aided Chlainne Lir ("Children of Lir") and Tochmarc Étaíne ("The Wooing of Étaín").

The Children of Lir (Irish: Oidheadh chloinne Lir) is a legend from Irish mythology. It is a tale from the post-Christianisation period that mixes magical elements such as druidic wands and spells with a Christian message of Christian faith bringing freedom from suffering.