Derrynane Abbey, Medieval abbey ruins on Abbey Island, County Kerry, Ireland.

Derrynane Abbey consists of ruins on a small island near Caherdaniel, with three lancet windows facing toward the Atlantic Ocean. The remains show three connected stone buildings that reflect different phases of medieval construction.

Founded by St. Fionan in the 6th century, the monastery gave Derrynane its Irish name, Doire Fhionain ("Fionan's wood"). It later became an Augustinian house when it adopted the Rule of St Augustine in the 12th century, and was probably a cell of the St Michael Ballinskelligs priory. It was never formally an abbey; the title comes from local usage.

The name Derrynane comes from Doire Fhionain, "Fionan's wood", after the saint credited with founding the monastery in the 6th century. The church and its graveyard hold the grave of Mary O'Connell, wife of Daniel O'Connell of nearby Derrynane House, and of the 19th-century Gaelic poet Tomás Rua Ó Súilleabháin.

Access to the island is only possible at low tide when the beach becomes passable. Visitors should check tide times before visiting and wear suitable footwear since the path crosses sand and rocks.

Despite the name, Derrynane was never an abbey: the German Wikipedia notes the title comes only from local usage. It was an early monastery linked by legend to St Fionan (Finnian of Clonard, 470–549), later adopting the Augustinian rule in the 12th century, and probably a cell of St Michael Ballinskelligs.