The Sayfo or Seyfo (Neo-Aramaic: ܣܝܦܐ lit.'sword'; see below), also known as the Assyrian genocide, was the mass slaughter and deportation of Syriac Christians (mostly belonging to the Syriac Orthodox Church, Church of the East, or Chaldean Catholic Church) in eastern regions of the Ottoman Empire, and neighbouring regions of Persia, committed by Ottoman troops and some Kurdish tribes during World War I. The Sayfo mostly occurred between June and October 1915, concurrently with and closely related to the Armenian genocide, although it is considered less systematic.

Assyrian women fleeing through the mountains, 1915

Mass killing of Assyrian civilians began during the Ottoman occupation of Persia from January to May 1915, during which massacres were committed by Ottoman irregulars and Kurdish tribes. In Bitlis Vilayet, Ottoman troops returning from Iran combined with local Kurdish tribes to massacre the local Christian population, including Assyrians. In mid-1915, Ottoman forces as well as Kurds jointly attacked the Assyrian tribes of Hakkari, driving them out by September. In Diyarbekir vilayet, governor Mehmed Reshid initiated a genocide encompassing all of the Christian religious groups in the vilayet, including Syriac Christians. Ottoman Assyrians living farther south in present-day Iraq were not subjected to mass killing.

At the 1919 Paris Peace Conference, the Assyro-Chaldean delegation stated that its losses were 250,000, about half its prewar population. The Sayfo is comparatively less well-studied than the Armenian genocide. Efforts to have the Sayfo formally recognized as a genocide began in the 1990s and have been spearheaded by the Assyrian diaspora. Several countries have recognized that Assyrians in the Ottoman Empire were victims of a genocide, but Turkey denies that an Assyrian genocide took place.