Castletownbere (Baile Chaisleáin Bhéarra in Irish) is a town in County Cork, Republic of Ireland. It is located on the southwest coast of Ireland, in West Cork, on Berehaven harbour. It is also known as Castletown Berehaven (locally just Castletown). The name of the town comes from Dunboy Castle, which was home to the O'Sullivan-Bere family.

The deep-water harbour was, up to the 19th century, much used by smugglers. From 1922 to 1938, Berehaven was one of three Treaty ports in the Irish Free State, UK sovereign bases maintained by the Royal Navy. Castletownbere is currently one of the 5 main fishing ports on the island of Ireland.

See also: List of towns in the Republic of Ireland