Which treaty or agreement defined the borders of the modern Turkish Republic?

The Treaty of Lausanne was a peace treaty negotiated during the Lausanne Conference of 1922–23 and signed in the Palais de Rumine, Lausanne, Switzerland, on 24 July 1923. It officially settled the conflict that had originally existed between the Ottoman Empire and the Allied French Republic, British Empire, Kingdom of Italy, Empire of Japan, Kingdom of Greece, and the Kingdom of Romania since the onset of World War I. The original text of the treaty is in French. It was the result of a second attempt at peace after the failed Treaty of Sèvres. The earlier treaty had been signed by all previous parties, except the Kingdom of Greece, but later rejected by the Turkish national movement who fought against its terms.

The Treaty of Lausanne ended the conflict and defined the borders of the modern Turkish Republic. In the treaty, Turkey gave up all claims to the remainder of the Ottoman Empire and in return the Allies recognized Turkish sovereignty within its new borders. It provided for the Greek-Turkish population exchange and allowed unrestricted civilian and military passage through the Turkish Straits.

The treaty was ratified by Turkey on 23 August 1923. It came into force on 6 August 1924, when the instruments of ratification were officially deposited in Paris. Turkey also formally ceded all claims on the Dodecanese Islands, Cyprus, Egypt and Sudan, Syria and Iraq; and (along with the Treaty of Ankara) settled the boundaries of the latter two nations.