Roscoff is a commune in the Finistère département of Brittany in northwestern France.
Roscoff is renowned for its picturesque architecture, labelled petite cité de caractère de Bretagne since 2009. Roscoff is also a traditional departure point for Onion Johnnies.
After lobbying by local economic leaders headed by Alexis Gourvennec, the French government agreed in 1968 to provide a deep-water port at Roscoff. Existing ferry operators were reluctant to take on the relatively long Plymouth/Roscoff crossing so Gourvennec and colleagues founded Brittany Ferries. Since the early 1970s Roscoff has been developed as a ferry port for the transport of Breton agricultural produce and for motor tourism. Brittany Ferries and Irish Ferries link Roscoff with both Ireland and the United Kingdom.
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, Roscoff is also a centre of post-cure, which gave rise to the concept of thalassotherapy in the latter half of the 19th century. A French doctor, Louis-Eugène Bagot, opened the Institut marin in Roscoff in 1899, the first centre for thalassotherapy in Europe.