Rothesay is the principal town on the Isle of Bute, in the council area of Argyll and Bute, Scotland. It lies along the coast of the Firth of Clyde. It can be reached by ferry from Wemyss Bay, which offers an onward rail link to Glasgow. At the centre of the town is the 13th-century ruin Rothesay Castle, unique in Scotland for its circular plan.

In modern Scottish Gaelic, Rothesay is known as Baile Bhòid, meaning 'town of Bute'. The English-language name, which was written as Rothersay in 1321, Rosay around 1400, and Rothissaye around 1500, originally referred to the castle. Since the castle was surrounded by a moat connected to the sea, the name may have originally meant 'Rother's Isle' (the Old Norse suffix -ey means "isle"), or it may be an alteration of the Gaelic word rath, meaning 'fort'.