The Princes' Islands (Turkish: Prens Adaları; the word "princes" is plural, because the name means "Islands of the Princes", Greek: Πριγκηπονήσια, Pringiponisia), officially just Adalar (English: Islands); 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 km (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.
Adalar District is made up of the main four islands (Büyükada, Kınalıada, Burgazada, and Heybeliada) and the other smaller islands.