The 1923 population exchange between Greece and Turkey stemmed from the "Convention Concerning the Exchange of Greek and Turkish Populations" signed at Lausanne, Switzerland, on 30 January 1923, by the governments of Greece and Turkey. It involved at least 1.6 million people (1,221,489 Greek Orthodox from Asia Minor, Eastern Thrace, the Pontic Alps and the Caucasus, and 355,000–400,000 Muslims from Greece), most of whom were forcibly made refugees and de jure denaturalized from their homelands.

The initial request for an exchange of population came from Eleftherios Venizelos in a letter he submitted to the League of Nations on 16 October 1922, as a way to normalize relations de jure, since the majority of surviving Greek inhabitants of Turkey had fled from recent massacres to Greece by that time. Venizelos proposed a "compulsory exchange of Greek and Turkish populations," and asked Fridtjof Nansen to make the necessary arrangements. Though prior to that, on 16 March 1922, the Turkish Minister of Foreign Affairs Yusuf Kemal Tengrişenk, had stated that "he Ankara Government was strongly in favour of a solution that would satisfy world opinion and ensure tranquillity in its own country", and that "t was ready to accept the idea of an exchange of populations between the Greeks in Asia Minor and the Muslims in Greece". The new state of Turkey also envisioned the population exchange as a way to formalize and make permanent the flight of its native Greek Orthodox peoples while initiating a new exodus of a smaller number (400,000) of Muslims from Greece as a way to provide settlers for the newly-depopulated Orthodox villages of Turkey; Greece meanwhile saw it as a way to provide propertyless Greek Orthodox refugees from Turkey with lands of expelled Muslims.

This major compulsory population exchange, or agreed mutual expulsion, was based not on language or ethnicity, but upon religious identity, and involved nearly all the indigenous Orthodox Christian peoples of Turkey (the Rûm "Roman/Byzantine" millet), including even Armenian- and Turkish-speaking Orthodox groups, and on the other side most of the native Muslims of Greece, including even Greek-speaking Muslim citizens, such as Vallahades and Cretan Turks, but also Muslim Roma groups, such as Sepečides. Each group were native peoples, citizens, and in cases even veterans, of the state which expelled them, and neither had representation in the state purporting to speak for them in the exchange treaty.