They consist of four larger islands, Büyükada ("Big Island") with an area of 5.46 km2 (2.11 sq mi), Heybeliada ("Saddlebag Island") with an area of 2.4 km2 (0.93 sq mi), Burgazada ("Fortress Island") with an area of 1.5 km2 (0.58 sq mi), Kınalıada ("Henna Island") with an area of 1.3 km2 (0.50 sq mi), and five much smaller ones, Sedef Adası ("Mother-of-Pearl Island") with an area of 0.157 km2 (0.061 sq mi), Yassıada ("Flat Island") with an area of 0.05 km2 (0.019 sq mi), Sivriada ("Sharp Island") with an area of 0.05 km2 (0.019 sq mi), Kaşık Adası ("Spoon Island") with an area of 0.006 km2 (0.0023 sq mi), and Tavşan Adası ("Rabbit Island") with an area of 0.004 km2 (0.0015 sq mi).
During the summer months the Princes' Islands are popular destinations for day trips from Istanbul. As there is no traffic on the Islands, the only transport being horse and cart, they are amazingly peaceful in contrast with the city of Istanbul. They are just a short ferry ride from Istanbul, with ferries departing from Bostancı, Kartal and Maltepe on the Asian side, and from Kabataş on the European side. Most ferries call in turn at the four largest of the nine islands: Kınalıada, Burgazada, Heybeliada, and, finally, Büyükada. Ferry and ship services are provided by six different companies. In spring and autumn the islands are quieter and more pleasant, although the sea can be rough in spring, autumn and winter, and the islands are sometimes cut off from the outside world when the ferry services are cancelled due to storms and high waves. During winter, with the addition of the biting cold and the strong winds and the resulting ferry cancellations, the islands become almost deserted. As for cultural tourism, Büyükada happens to have the first and only city museum in İstanbul, the Museum of the Princes' Islands in Aya Nikola Bay.
During the Byzantine period, princes and other royalty were exiled on the islands, and later members of the Ottoman sultans family were exiled there too, giving the islands their present name. They were taken by the Ottoman fleet during the siege of Constantinople in 1453. During the nineteenth century, the islands became a popular resort for Istanbul's wealthy, and Victorian-era cottages and houses are still preserved on the largest of the Princes' Islands.
The Halki seminary, formally the Theological School of Halki (Greek: Θεολογική Σχολή Χάλκης and Turkish: Ortodoks Ruhban Okulu), was founded on 1 October 1844 on the island of Halki (Turkish: Heybeliada), the second-largest of the Princes' Islands in the Sea of Marmara. It was the main school of theology of the Eastern Orthodox Church's Ecumenical Patriarchate of Constantinople until the Turkish parliament enacted a law banning private higher education institutions in 1971. The theological school is located at the top of the island's Hill of Hope, on the site of the Byzantine-era Monastery of the Holy Trinity. The premises of the school continue to be maintained by the monastery and are used to host conferences. It is possible to visit the island where it is located via boat in approximately one hour from the shore of Istanbul.
In 1912 on the islands lived 10 250 Greeks and 670 Turks. The islands have become more and more ethnically Turkish in character due to the influx of wealthy Turkish jetsetters, a process which began in the first days of the Turkish Republic when the British Yacht Club on Büyükada was appropriated as Anadolu Kulübü, for Turkish parliamentarians to enjoy Istanbul in the summer. The islands are an interesting anomaly because they allow for a very rare, albeit incomplete, insight into a multicultural society in modern Turkey, possibly akin to the multicultural society that once existed during the Ottoman Empire in places such as nearby Istanbul/Constantinople. Prior to the 1950s, each of the inhabited islands had significant communities of ethnic minorities of Turkey, which is now the case to a much smaller extent. Since the vast majority of the residents and visitors are Turkish, today their legacy is of cultural rather than demographic importance.