The Princes' Islands, officially just Adalar ; alternatively the Princes' Archipelago; is an archipelago of nine islands off the coast of Istanbul, Turkey, in the Sea of Marmara. These constitute the municipality and district of Adalar within Istanbul Province. With a total land area of 11 km2 (4.2 sq mi), it is the fifth smallest district in Istanbul and, with a permanent population of 16,690 (2022), by far the least populous district in Istanbul.