Minorities in Turkey form a substantial part of the country's population, representing an estimated 25 to 28 percent of the population. Historically, in the Ottoman Empire, Islam was the official and dominant religion, with Muslims having more rights than non-Muslims, whose rights were restricted. Non-Muslim (dhimmi) ethno-religious groups were legally identified by different millet ("nations").

Following the end of World War I and the dissolution of the Ottoman Empire, all Ottoman Muslims were made part of the modern citizenry or the Turkish nation as the newly founded Republic of Turkey was constituted as a Muslim nation state. While Turkish nationalist policy viewed all Muslims in Turkey as Turks without exception, non-Muslim minority groups, such as Jews and Christians, were designated as "foreign nations" (dhimmi). Conversely, Turk (term for Muslims) was used to denote all groups in the region who had been Islamized under Ottoman rule, especially Muslim Albanians and Slavic Muslims.

The 1923 Treaty of Lausanne specified Armenians, Greeks and Jews and Christians in general as ethnic minorities (dhimmi). This legal status was not granted to Muslim minorities, such as the Kurds, which constituted the largest minority by a wide margin, nor any of the other minorities in the country. In modern Turkey, data on the ethnic makeup of the country is not officially collected, although various estimates exist. All Muslim citizens are still regarded as Turks by law, regardless of their ethnicity or language, in contrast to non-Muslim minorities, who are still grouped as "non-Turks"; the largest ethnic minority, the Kurds, who are predominantly Muslim, are therefore still classified as simply "Turks". Bulgarians are also an officially recognized minority by the Turkey-Bulgaria Friendship Treaty (Türkiye ve Bulgaristan Arasındaki Dostluk Antlaşması) of 18 October 1925 but in the present day there are only a few hundred Bulgarians in Turkey. On 18 June 2013, the Ankara 13th Circuit Administrative Court unanimously ruled that the Assyrians were included as beneficiaries of the Lausanne Treaty, so that Assyrians were allowed to open the first school teaching in their mother tongue.

The amount of ethnic minorities is considered to be underestimated by the Turkish government. Therefore, the exact number of members of ethnic groups who are Muslim is unknown; these include Arabs, Albanians, Bosniaks, Circassians, Chechens, Abkhazians, Crimean Tatars, Laz, Hemshin Armenians, Kurds, Pomaks, Turkish Roma, and Pontic Greeks, among other smaller groups like Dom, Lom, Vallahades, Greek Muslims, Cretan Muslims, Nantinets, Imerkhevians. Many of the non-Turkish Muslim minorities are descendants of Muslims (muhajirs) who were expelled from the lands lost by the shrinking Ottoman Empire, like the Balkans and Caucasus Mountains. The majority have assimilated into and intermarried with the majority Turkish population and have adopted the Turkish language and way of life, though do not necessarily identify as Turks, especially the Pomaks. Turkification and often aggressive Turkish nationalist policies strengthen these trends.^{[citation needed]}

Groups of nomadic and semi-nomadic itinerants found mainly in central and western Anatolia. They speak an argot of their own and are Alevis.

Afghans are one of the largest irregular migrant groups in Turkey. From the period 2003–2007, the number of Afghans apprehended were significant, with statistics almost doubling during the last year. Most had fled the War in Afghanistan. In 2005, refugees from Afghanistan numbered 300 and made a sizeable proportion of Turkey's registered migrants. Most of them were spread out over satellite cities with Van and Ağrı being the most specific locations. In the following years, the number of Afghans entering Turkey greatly increased, second only to migrants from Iraq; in 2009, there were 16,000 people designated under the Iraq-Afghanistan category. Despite a dramatic 50 percent reduction by 2010, reports confirmed hundreds living and working in Turkey. As of January 2010, Afghans consisted one-sixth of the 26,000 remaining refugees and asylum seekers. By the end 2011, their numbers are expected to surge up to 10,000, making them the largest population and surpass other groups.

Beginning several centuries ago, a number of Africans, usually via Zanzibar as Zanj and from places such as Niger, Saudi Arabia, Libya, Kenya and Sudan, came to the Ottoman Empire settled by the Dalaman, Menderes and Gediz valleys, Manavgat, and Çukurova. African quarters of 19th-century İzmir, including Sabırtaşı, Dolapkuyu, Tamaşalık, İkiçeşmelik, and Ballıkuyu, are mentioned in contemporary records. Due to the slave trade in the Ottoman Empire that had flourished in the Balkans, the coastal town of Ulcinj in Montenegro had its own black community. As a consequence of the slave trade and privateer activity, it is told how until 1878 in Ulcinj 100 black people lived. The Ottoman Army also deployed an estimated 30,000 Black African troops and cavalrymen to its expedition in Hungary during the Austro-Turkish War of 1716–18.

A 2008 report from the Turkish National Security Council (MGK) estimated that approximately 1.3 million people of Albanian ancestry live in Turkey, and more than 500,000 recognizing their ancestry, language and culture. There are other estimates, however, that place the number of people in Turkey with Albanian ancestry and or background upward to 5 million.