Christianity in Turkey has a long history, dating back to the early origins of Christianity in Asia Minor and the Middle East during the 1st century AD. In modern times the percentage of Christians in Turkey has declined from 20 to 25% in 1914, to about 2% in 1927, to 0.2–0.4% today. Sources estimate that the Christian population in Turkey ranges between 203,500 and more than 370,000. However, the exact number remains unclear due to the absence of a religious census in the country. The percentage of Christians in Turkey fell mainly as a result of the late Ottoman genocides: the Armenian genocide, Greek genocide, and Assyrian genocide, the population exchange between Greece and Turkey, the emigration of Christians that began in the late 19th century and gained pace in the first quarter of the 20th century, and due to events such as the 1942 Varlık Vergisi tax levied on non-Muslim citizens in Turkey and the 1955 Istanbul pogrom against Greek and Armenian Christians. Exact numbers are difficult to estimate, as many Turkish former Muslim converts to Christianity often hide their Christian faith for fear of familial pressure, religious discrimination, and persecution.
This was due to events which had a significant impact on the country's demographic structure, such as the First World War, the anti-Christian genocides of Greeks, Armenians, and Assyrians perpetrated by Turkish Muslims, and the population exchange between Greece and Turkey, and the emigration of persecuted Christians (such as Assyrians, Greeks, Armenians, etc.) to foreign countries (mostly in Europe and the Americas) that began in the late 19th century and gained pace in the first quarter of the 20th century, especially during World War I. Signed after the First World War, the Treaty of Lausanne explicitly guarantees the security and protection of both Greek and Armenian Orthodox Christian minorities. Their religious institutions are recognized officially by the Republic of Turkey.