They comprise legends about historical and semi-historical kings of Ireland (such as Buile Shuibhne, "The Madness of King Suibhne"), stories about the origins of dynasties and peoples (such as The Expulsion of the Déisi), accounts of significant battles (such as Battle of Mag Mucrama), as well as anecdotes that explain rites and customs.
It was part of the duty of the medieval Irish bards, or court poets, to record the history of the family and the genealogy of the king they served.
One of the most famous legends is the Buile Shuibhne, a 12th-century tale told in verse and prose.
Suibhne, king of Dál nAraidi, was cursed by St Ronan Finn and became a kind of half-man, half-bird, condemned to live out his life in the woods, fleeing from his human companions.
The story has captured the imaginations of contemporary Irish poets and has been translated by Trevor Joyce and Seamus Heaney.