The Treaty of Lausanne (French: Traité de 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. The treaty 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 and unratified Treaty of Sèvres, which aimed to divide Ottoman lands. The earlier treaty had been signed in 1920, but later rejected by the Turkish national movement who fought against its terms. As a result of Greco-Turkish War, İzmir was retrieved and Armistice of Mudanya was signed in October 1922. It provided for the Greek-Turkish population exchange and allowed unrestricted civilian passage through the Turkish Straits (but not military).

The treaty was ratified by Turkey on 23 August 1923, and all of the other signatories by 16 July 1924. It came into force on 6 August 1924, when the instruments of ratification were officially deposited in Paris.A Declaration of Amnesty granted immunity for crimes committed between 1914 and 1922, notably the Armenian genocide. Historian Hans-Lukas Kieser states, "Lausanne tacitly endorsed comprehensive policies of expulsion and extermination of hetero-ethnic and hetero-religious groups".