Islam

Islam is by far the most practiced religion in Turkey. Most Turkish people are Sunni Muslims, and most of them belong to the Hanafi school of jurisprudence. Smaller numbers belonging to the Alevi, Ja'fari and Alawite minorities. The established presence of Islam in the region that now constitutes modern Turkey dates back to the later half of the 11th century, when the Seljuks started expanding into eastern Anatolia.

While official records indicate the population of Turkey to be 99.8% Muslim, most surveys estimate the percentage to be around 85 to 95%. The Hanafi school of fiqh (maddhab) of Sunni Islam makes up about 90% of the Muslim population, with the remaining Muslim sects consisting of Alevis (close to 10%), Ja'faris (representing 1%) and Alawites (with an estimated population of around 500,000 to 1 million, or about 1%). With a sizeable part of population being Cultural Muslims, there is also a minority of Sufi and non-denominational Muslims.

The ethnonym Turk (Greek: Τούρκοι/Tourkoi, Serbo-Croatian: Turci/Турци, Macedonian: Турчин, Bulgarian: Турчин, Albanian: Turqit) has been commonly used by the non-Muslim Balkan peoples to denote all Muslim people in the region, regardless of their ethno-linguistic background. Most of the Muslims in the Ottoman Empire, however, were indeed ethnic Turks. In the Ottoman Empire, the faith of Islam was the official state religion, with Muslims holding higher rights than non-Muslims. Non-Muslim (dhimmi) ethno-religious legal groups were identified by different millets ("nations").

Turk was also notably used to denote all groups in the region who had been Islamized during the Ottoman rule, especially Muslim Albanians and Slavic Muslims (mostly Bosniaks). For the Balkan Christians, converting to Islam was synonymous with Turkification, succumbing to "Ottoman rule and embracing the Ottoman way of life," hence "to become a Turk". In South Slavic languages, there are also derivative terms, which are seen as more offensive towards Bosniaks, such as poturiti, poturčiti and poturica (all essentially meaning "Turk" or "to turkify").

The spread of Islam spans almost 1,400 years. The early Muslim conquests that occurred following the death of Muhammad in 632 CE led to the creation of the caliphates, expanding over a vast geographical area; conversion to Islam was boosted by Arab Muslim forces expanding over vast territories and building imperial structures over time. Most of the significant expansion occurred during the reign of the rāshidūn ("rightly-guided") caliphs from 632 to 661 CE, which were the first four successors of Muhammad. These early caliphates, coupled with Muslim economics and trading, the Islamic Golden Age, and the age of the Islamic gunpowder empires, resulted in Islam's spread outwards from Mecca towards the Indian, Atlantic, and Pacific Oceans and the creation of the Muslim world. The Islamic conquests, which culminated in the Arab empire being established across three continents (Asia, Africa, and Europe), enriched the Muslim world, achieving the economic preconditions for the emergence of this institution owing to the emphasis attached to Islamic teachings. Trade played an important role in the spread of Islam in some parts of the world, such as Indonesia. During the early centuries of Islamic rule, conversions in the Middle East were mainly individual or small-scale. While mass conversions were favored for spreading Islam beyond Muslim lands, policies within Muslim territories typically aimed for individual conversions to weaken non-Muslim communities. However, there were exceptions, like the forced mass conversion of the Samaritans.

Muslim dynasties were soon established and subsequent empires such as those of the Umayyads, Abbasids, Mamluks, Seljukids, and the Ayyubids were among some of the largest and most powerful in the world. The Ajuran and Adal Sultanates, and the wealthy Mali Empire, in North Africa, the Delhi, Deccan, and Bengal Sultanates, and Mughal and Durrani Empires, and Kingdom of Mysore and Nizam of Hyderabad in the Indian subcontinent, the Ghaznavids, Ghurids, Samanids in Persia, Timurids, and the Ottoman Empire in Anatolia significantly changed the course of history. The people of the Islamic world created numerous sophisticated centers of culture and science with far-reaching mercantile networks, travelers, scientists, hunters, mathematicians, physicians, and philosophers, all contributing to the Islamic Golden Age. The Timurid Renaissance and the Islamic expansion in South and East Asia fostered cosmopolitan and eclectic Muslim cultures in the Indian subcontinent, Malaysia, Indonesia and China. The Ottoman Empire, which controlled much of the Middle East and North Africa in the early modern period, also did not officially endorse mass conversions, but evidence suggests they occurred, particularly in the Balkans, often to evade the jizya tax. Similarly, Christian sources mention requests for mass conversions to Islam, such as in Cyprus, where Ottoman authorities refused, fearing economic repercussions.

A state religion (also called official religion) is a religion or creed officially endorsed by a sovereign state. A state with an official religion (also known as a confessional state), while not a secular state, is not necessarily a theocracy. State religions are subject to advantageous treatment by official or government-sanctioned establishments of them, ranging from incentivising citizens to recognise and practice them through government endorsement to having public spending on the maintenance of religious property and clergy be unrestricted, but the state does not need to be under the legislative control of the clergy as it would be in a theocracy. Generally, these religions have more rights and fewer restrictions in the country than other religions in a country.

Official religions have been known throughout human history in almost all types of cultures, reaching into the Ancient Near East and prehistory. The relation of religious cult and the state was discussed by the ancient Latin scholar Marcus Terentius Varro, under the term of theologia civilis (lit. 'civic theology'). The first state-sponsored Christian denomination was the Armenian Apostolic Church, established in 301 CE. In Christianity, as the term church is typically applied to a place of worship for Christians or organizations incorporating such ones, the term state church is associated with Christianity as sanctioned by the government, historically the state church of the Roman Empire in the last centuries of the Empire's existence, and is sometimes used to denote a specific modern national branch of Christianity. Closely related to state churches are ecclesiae, which are similar but carry a more minor connotation.

Sunni Islam is the largest branch of Islam and the largest religious denomination in the world. It holds that Muhammad did not appoint any successor and that his closest companion Abu Bakr (r. 632–634) rightfully succeeded him as the caliph of the Muslim community, being appointed at the meeting of Saqifa. This contrasts with the Shia view, which holds that Muhammad appointed Ali ibn Abi Talib (r. 656–661) as his successor. Nevertheless, Sunnis revere Ali, along with Abu Bakr, Umar (r. 634–644) and Uthman (r. 644–656) as 'rightly-guided caliphs'.

The term Sunni means those who observe the sunna, the practices of Muhammad. The Quran, together with hadith (especially the Six Books) and ijma (scholarly consensus), form the basis of all traditional jurisprudence within Sunni Islam. Sharia legal rulings are derived from these basic sources, in conjunction with consideration of public welfare and juristic discretion, using the principles of jurisprudence developed by the four legal schools: Hanafi, Hanbali, Maliki and Shafi'i.

Islamic schools and branches have different understandings of Islam. There are many different sects or denominations, schools of Islamic jurisprudence, and schools of Islamic theology, or ʿaqīdah (creed). Within Sunnī Islam, there may be differences, such as different orders (tariqa) within Sufism, different schools of theology (Atharī, Ashʿarī, Māturīdī) and jurisprudence (Ḥanafī, Mālikī, Shāfiʿī, Ḥanbalī). Groups in Islam may be numerous (Sunnīs make up 87-90% of all Muslims), or relatively small in size (Ibadis, Ismāʿīlīs, Zaydīs).

Differences between the groups may not be well known to Muslims outside of scholarly circles, or may have induced enough passion to have resulted in political and religious violence (Barelvism, Deobandism, Salafism, Wahhabism). There are informal movements driven by ideas (such as Islamic modernism and Islamism), as well as organized groups with governing bodies (such as Nation of Islam). Some of the Islamic sects and groups regard certain others as deviant or not being truly Muslim (for example, Sunnīs frequently discriminate against Ahmadiyya, Alawites, Quranists, and sometimes Shīʿas). Some Islamic sects and groups date back to the early history of Islam between the 7th and 9th centuries CE (Kharijites, Mu'tazila, Sunnīs, Shīʿas), whereas others have arisen much more recently (Islamic neo-traditionalism, liberalism and progressivism, Islamic modernism, Salafism and Wahhabism), or even in the 20th century (Nation of Islam). Still others were influential historically, but are no longer in existence (non-Ibadi Kharijites and Murji'ah).

Sufism (Arabic: الصوفية‎, romanized: aṣ-Ṣūfiyya or Arabic: التصوف‎, romanized: at-Taṣawwuf) is a mystic body of religious practice found within Islam which is characterized by a focus on Islamic purification, spirituality, ritualism, and asceticism.

Practitioners of Sufism are referred to as "Sufis" (from صُوفِيّ, ṣūfīy), and historically typically belonged to "orders" known as tariqa (pl. turuq) — congregations formed around a grand wali (saint) who would be the last in a chain of successive teachers linking back to Muhammad, with the goal of undergoing tazkiya (self purification) and the hope of reaching the spiritual station of ihsan. The ultimate aim of Sufis is to seek the pleasure of God by endeavoring to return to their original state of purity and natural disposition, known as fitra.

The Ottoman Caliphate (Ottoman Turkish: خلافت مقامى, romanized: hilâfet makamı, lit. 'office of the caliphate') was the claim of the heads of the Turkish Ottoman dynasty, rulers of the Ottoman Empire, to be the caliphs of Islam during the late medieval and early modern era.

Ottoman rulers first assumed the style of caliph in the 14th century, though did at that point not claim religious authority beyond their own borders. After the conquest of Mamluk Egypt by Sultan Selim I in 1517 and the abolition of the Mamluk-controlled Abbasid Caliphate, Selim and his successors ruled one of the strongest states in the world and gained control of Mecca, Medina and Jerusalem, the religious and cultural centers of Islam. The claim to be caliphs transitioned into a claim to universal caliphal authority, similar to that held by the Abbasid Caliphate prior to the sack of Baghdad in 1258. Further Ottoman victories, the dynasty's geopolitical dominance in the 16th–17th centuries, and the lack of rival claimants strengthened the Ottoman claim to be the leaders of the Muslim world.

Religion in Greece is dominated by Christianity, in particular the Greek Orthodox Church, which is within the larger communion of the Eastern Orthodox Church. It represented 81 to 90% of the total population in 2022 and is constitutionally recognized as the "prevailing religion" of Greece. Religions with smaller numbers of followers include Islam followed by different communities of Greek Muslims (now comprising only 2% of the population), Western Catholicism (comprising 1% of the population), Greek Catholicism, Judaism, Evangelicalism, Hellenic paganism, and Jehovah's Witnesses. A number of Greek atheists exist, not self-identifying as religious.