Aidhne also known as, Uí Fhiachrach Aidhne, Maigh Aidhne / Maigh nAidhne ('Plain (of) Aidhne') was the territory of the Ui Fiachrach Aidhne, a tuath (tribal kingdom) located in the south of what is now County Galway in the south of Connacht, Ireland. Aidhne is coextensive with the present diocese of Kilmacduagh. The territory of Aidhne is bounded on the west by Loch Lurgain (Galway Bay) and the district of Burren in County Clare in the province of Munster. County Clare also bounds Aidhne on its south and south-east side. Aidhne is bounded on the east by the low mountains of Sliabh Echtghe / Slieve Aughty, which separate Uí Fhiachrach Aidhne from the territory of Uí Mhaine in eastern County Galway. On the north-east Aidhne is bounded by the plains of Uí Mhaine and on the north by Maigh Mucruimhe (the area around Athenry). On the north-west Aidhne is bounded by the parish of Meadhraighe / Maree which is in the territory of Uí Bhriúin Seola.
In placename lore the kingdom took its name from the mythological Aidhne, one of the ten daughters of Partholon by his first wife, Topha. Aidhne was married to Breac.
In a later age, a branch of the Fir Bolg made Aidhne their home. Dubhaltach Mac Fhirbhisigh's Book of Genealogies states that the Tuath mhac nUmhoir[settled in]in Dál gCais and in Ui Fhiachrach of Aidhne. Their leader is given as Conall Caol, son of Aonghus mac Úmhór. Connall was killed at the Battle of Maigh Mucruimhe in 195 A.D., and his body brought back to Aidhne where it was interred at a leacht called Carn Connell (itself the site of a major battle some centuries later).
The territory of Uí Fhiachrach Aidhne is coextensive with the diocese of Cill Mhic Dhuach / Kilmacduagh, which contains the civil parishes of Kinvarradoorus, Killinny, Killeenavarra, Drumacoo, Kilcolgan, Ardrahan, Stradbally, Killeeneen, Killeely, Killora, Killogilleen, Kilchreest, Isertkelly, Killinan, Kilthomas, Kilbeacanty, Beagh, Kilmacduagh, Kiltartan. The diocese of Kilmacduagh contains the present Catholic parishes of Kinvara, Ballinderreen, Gort, Ardrahan, Craughwell, Beagh, Kilbeacanty, Kilthomas (Peterswell), Clarinbridge, Kilchreest.