Roscoff (/ˈrɒskoʊ/ ROSK-oh, French: [ʁɔskɔf]; Breton: Rosko) is a commune in the Finistère département of Brittany in northwestern France.

After lobbying by local economic leaders headed by Alexis Gourvennec, the French government agreed in 1968 to provide a deep-water port at Roscoff.

Since the early 1970s Roscoff has been developed as a ferry port for the transport of Breton agricultural produce and for motor tourism.

Owing to the richness of iodine in the surrounding waters and the mild climate maintained by a sea current that varies only between 8 and 18 °C (46 and 64 °F), Roscoff is also a centre of post-cure, which gave rise to the concept of thalassotherapy in the latter half of the 19th century.

The nearby Île de Batz, called Enez Vaz in Breton, is a small island that can be reached by launch from the harbour.