Clare Island Abbey, Former Cistercian abbey and National Monument in County Mayo, Ireland

Clare Island Abbey is a ruined Cistercian monastery in the centre of the south of Clare Island, County Mayo. Its church is a single nave without a transept, with a chancel separated by an arch; the ruined nave was secured and given a new roof during conservation work between 1990 and 2000. Inside are a piscina, sedilia, carved heads and ogee and cusp-headed lancet windows.

The monastery was founded in the 13th century and became associated with Knockmoy Abbey, showing the interconnection of religious communities in the region. Around 1460, the O'Malley family undertook significant reconstruction work on the site, reflecting their power and influence.

The interior walls display medieval paintings of dragons, stags, and musicians that reflect the artistic traditions of the period. These wall paintings offer insight into how religious spaces were decorated during the Middle Ages, counting among Ireland's rare surviving examples.

The abbey is accessible by ferry from Roonagh Pier to Clare Island, followed by a short walk west from the pier. Visitors should expect uneven ground and wear suitable footwear since the ruins sit on open terrain.

Tradition holds that Gráinne "Grace" O'Malley, the Connacht sea trader and clan leader (c. 1530 – c. 1603), was baptised, married and buried here, and she is said to lie in the canopied O'Malley tomb. The abbey also keeps medieval wall and ceiling paintings of dragons, a cockerel, stags, a harper and horsemen, ornamentation unusual for a Cistercian foundation.