The Princes' Islands (Turkish: Kızıl Adalar or just Adalar, meaning "(Red) Islands", classical Greek: Prinkēpōn nēsoi, Πριγκήπων νήσοι, modern Greek: Prinkiponisia, Πριγκηπονήσια), are a chain of nine islands off the coast of Istanbul, Turkey, in the Sea of Marmara. The largest island is Büyükada (Greek: Prinkipo, "Πρίγκηπος" meaning "Prince"), the four other sizable islands being Burgazada (Greek: Antigoni), Heybeliada (Greek: Halki), Kınalıada (Greek: Proti, Πρώτη, meaning "The First"(island)) and Sedef Adası (Greek: Terebinthos).

The pine – forested Princes’ Islands provide a welcome break from the bustle of the city and are just a short ferry ride southeast from Istanbul. In 2003, a large portion of the pine forests on Burgazada burnt down. Most ferries call in turn at the four largest of the nine islands: Kınalıada, Burgazada, Heybeliada and finally Büyükada.

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, lending the islands their present name. During the 19th 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 Princes' 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. However, the Greek, Armenian and Jewish communities still constitute a small part of the islands' population. The islands are an interesting anomaly because they allow us to have a rare and incomplete insight into a multicultural society in modern Turkey, possibly alike to the multicultural society that once existed during the Ottoman Empire in places such as nearby Istanbul/Constantinople

During the summer months the Islands are popular destinations for day trips via ferry from both the Asian (at Bostancı and also Kartal) and European sides (from Sirkeci/Eminönü, Kabatas and Yenikapi) of Istanbul. Ferry services are provide by Istanbul Sea Buses, a firm operated by the municipality of Istanbul.

Büyükada (Prinkipo)
The once flourishing luxury hotel trade on Büyükada has declined. Previous generations would come for swimming, but today the Marmara Sea is not clean enough to really enjoy the beaches at the back of the island. But the island is gorgeous (especially in spring when the trees are in blossom). As on most of the other islands, motorized vehicles – except service vehicles – are forbidden, so visitors explore the island by foot, bicycle, in horse-drawn carriages, or by riding donkeys.

A convent on Büyükada was the place of exile for the Byzantine empresses Irene, Euphrosyne, Zoe and Anna Dalassena. After his deportation from the Soviet Union in February 1929, Leon Trotsky also stayed for four years on Büyükada, his first station in exile. Princess Fahrelnissa Zeid was born in the island.

There are several historical buildings on Büyükada, such as the Ayia Yorgi Church and Monastery dating back to the 6th century, the Ayios Dimitrios Church, and the Hamidiye Mosque built by Abdul Hamid II. Büyükada consists of two peaks. The one nearest to the iskele (ferry landing), Hristos, is topped by the former Greek Orphanage, a huge wooden building now in decay. In the valley between the two hills sit the church and monastery of Ayios Nikolaos and a former fairground called Luna Park. Visitors can take the 'small tour' of the island by buggy, leading to this point, from where it is an easy climb to Ayia Yorgi, a tiny church with a cafe on the grounds serving wine, chips and sausage sandwiches, this being part of the "classic" Ayia Yorgi (St. George, in Greek Άγιος Γεώργιος) experience.

Heybeliada (Halki)
Heybeliada is the second largest of the Islands, consisting of four hills. The large Naval Cadet School overlooks the jetty to the left as you get off the ferry. There are two interesting pieces of architecture on the grounds of the school. One is Kamariotissa, the only Byzantine church on the island, and more importantly the last church to be built before the conquest of Constantinople. The other is the grave of the second English Ambassador to be sent to Constantinople by Elisabeth I of England, Edward Barton, who chose to live on Heybeli to escape the bustle of the city. To the right of the jetty lies the town with its bars and cafes, a hotel that stays open all year round, and many lovely wooden houses. On one of the hills can be found the monastery of Ayia Trias (Holy Trinity), which houses the Halki seminary, until recently the main Greek Orthodox seminary in Turkey and Theological Seminary of the Patriarchate before it was closed down by the Turkish government.

Burgazada (Antigoni)
Burgazada is the third largest of the Islands, a single hill 2 kilometres across. Demetrius I of Macedon, one of the Diadochi (Successors) of Alexander the Great, built a fort here and named it after his father Antigonus I Monophthalmus. The island took this name, but today is generally known by Turks simply as "Burgaz" (Turkish for "fort"). In 2003 Burgaz suffered a terrible forest fire, losing 4 square kilometres of woodland.

Kınalıada (Proti)
Kınalıada (meaning "Henna Island") is the nearest island to the European side of Istanbul (about an hour by ferry from Sirkeci). This therefore was the island most used as a place of exile in Byzantine times (the most notable exile being the former emperor Romanos IV Diogenes, after the Battle of Manzikert, 1071). This is one of the least forested islands, and the land has a reddish colour from the iron and copper that has been mined here.

Yassıada and Sivriada
Of the two small islands further off shore, Yassıada was for many years the property of the Turkish Navy and today belongs to Istanbul University. In earlier times, British ambassador Henry Bulwer, brother of novelist Edward Bulwer-Lytton, built himself a mansion here to live undisturbed on this distant island. It is also where the trials of the members of the former ruling party, Demokrat Partı, were held after the military coup of 1960. Several of the defendants were sentenced to death, and three of these, including the former Prime Minister of Turkey Adnan Menderes, were executed.

Sivriada meanwhile is still deserted. In the last days of Ottoman rule a governor of Istanbul ordered the wild dogs in the streets to be gathered and deposited here. There is nothing there today but the ruins of a monastery which can be seen on the shore.