Since the foundation of the Republic of Turkey, its official armed and paramilitary forces have committed numerous violations of international criminal law (including war crimes, crimes against humanity and the crime of genocide), and are also accused of aiding and abetting crimes committed by non-state actors, including rebel groups in Syria. Turkish war crimes have included massacres, torture, terrorism, deportation or forced displacement, kidnapping, sexual violence, looting, unlawful confinement, unlawful airstrikes and indiscriminate attacks on civilian structures.

The founders of the modern Turkish nation-state, who led the nationalist movement in the years following World War I, committed numerous atrocities during the War of Independence and continued many of the late Ottoman Empire's genocidal policies against Christian minorities, especially Armenians and Greeks. After its formal establishment in 1923, the Turkey would perpetrate many human rights violations against Kurds (both inside and outside its borders) during the long running Kurdish–Turkish conflict. Turkey has faced many accusations of committing war crimes in other countries, including in Cyprus, Syria and Libya.

War crimes are defined as acts which violate the laws and customs of war established by the Hague Conventions of 1899 and 1907, or acts that are grave breaches of the Geneva Conventions and Additional Protocol I and Additional Protocol II. The Fourth Geneva Convention of 1949 extends the protection of civilians and prisoners of war during military occupation, even if there is no armed resistance, for the period of one year after the end of hostilities. However, the occupying power should still be bound by several provisions of the convention as long as "such Power exercises the functions of government in such territory."

In the final years of the Ottoman Empire's existence, the Committee of Union and Progress (CUP) – the Turkish nationalist political party that ruled over it – committed a genocide against the empire's Armenian population. The Ottomans carried out organised, systematic massacres and deportations of Armenians throughout World War I, and they portrayed acts of resistance by Armenians as rebellions in an attempt to justify their extermination campaign. In early 1915, a number of Armenians volunteered to join the Russian forces, and the Ottoman government used this as a pretext to issue the Tehcir Law (Law on Deportation), which authorised the deportation of Armenians from the Empire's eastern provinces to Syria between 1915 and 1918. The Armenians were intentionally marched to death, and a large number of them were attacked by Ottoman brigands. While the exact number of deaths is unknown, the International Association of Genocide Scholars estimates that 1.5 million Armenians were killed. The Ottoman Empire repeatedly denied the genocide was happening, and the government of Turkey has continued these denials, arguing that those who died were victims of inter-ethnic fighting, famine, or disease during World War I; these claims are rejected by most historians.

Other ethnic groups were also attacked by the Ottoman Empire during this period, including Assyrians and Greeks, and some scholars consider those events different parts of the same policy of extermination. An estimated 250,000 Assyrian Christians (about half of the population) and 350,000–750,000 Greeks were killed between 1915 and 1922. According to Rudolph Rummel, during 1900 and 1923, the Turks massacred between 3,500,000 and 4,300,000 Christian Greek, Armenian, Assyrian and other Christian groups.

Vahagn Avedian argues that the Turkish War of Independence was not directed against the Allied Powers, but that its main objective was to get rid of non-Turkish minority groups. The Turkish National Movement, led by Mustafa Kemal Atatürk, maintained the aggressive policies of the CUP against Christians; most former members of the CUP joined the movement, and were active participants in the war.

Raymond Kévorkian states that "removing non-Turks from the sanctuary of Anatolia" was among the main activities of the Turkish Nationalists after World War I. Preventing Armenians and other Christians from returning home, and therefore allowing their properties to be retained by those who had stolen them during the war, was a key factor in securing popular support for the Turkish National Movement. Christian civilians were subjected to forced deportation to expel them from the country, a policy that continued after the war. These deportations were similar to those employed during the Armenian genocide, and caused many deaths. Many Greek men were conscripted into unarmed labor battalions where the death rate sometimes exceeded 90 percent. Over 1 million Greeks were expelled (as were all remaining Armenians in the areas of Diyarbekir, Mardin, Urfa, Harput, and Malatia), forced across the border into French-mandated Syria.

Historian Erik Sjöberg said that "It seems, in the end, unlikely that the Turkish Nationalist leaders, though secular in name, ever had any intention of allowing any sizeable non-Muslim minority to remain."