Islamic schools and branches in the context of "Sunnah"

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.

The terms Islamic world and Muslim world commonly refer to the Islamic community, which is also known as the Ummah. This consists of all those who adhere to the religious beliefs, politics, and laws of Islam or to societies in which Islam is practiced. In a modern geopolitical sense, these terms refer to countries in which Islam is widespread, although there are no agreed criteria for inclusion. The term Muslim-majority countries is an alternative often used for the latter sense.

The history of the Muslim world spans about 1,400 years and includes a variety of socio-political developments, as well as advances in the arts, science, medicine, philosophy, law, economics and technology during the Islamic Golden Age. Muslims look for guidance to the Quran and believe in the prophetic mission of the Islamic prophet Muhammad, but disagreements on other matters have led to the appearance of different religious schools of thought and sects within Islam. The Islamic conquests, which culminated in the Caliphate 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. In the modern era, most of the Muslim world came under European colonial domination. The nation states that emerged in the post-colonial era have adopted a variety of political and economic models, and they have been affected by secular as well as religious trends.

Sufi philosophy includes the schools of thought unique to Sufism, the mystical tradition within Islam, also termed as Tasawwuf or Faqr according to its adherents. Sufism and its philosophical tradition may be associated with both Sunni and Shia branches of Islam. It has been suggested that Sufi thought emerged from the Middle East in the eighth century CE, but adherents are now found around the world.

According to Sufi Muslims, it is a part of the Islamic teaching that deals with the purification of inner self and is the way which removes all the veils between the divine and humankind. It was around 1000 CE that early Sufi literature, in the form of manuals, treatises, discourses and poetry, became the source of Sufi thinking and meditations. Sufi philosophy, like all other major philosophical traditions, has several sub-branches, including cosmology and metaphysics, as well as several unique concepts.

The issue of succession following the death of the Islamic prophet Muhammad is the central issue in the schisms that divided the early Muslim community in the first century of Islamic history into numerous schools and branches. The two most prominent branches that emerged from these divisions are Sunni and Shia as well as Ibadi branches of Islam. Sunni Islam and Ibadi Islam asserts that Abu Bakr rightfully succeeded Muhammad through a process of election. In contrast, Shia Islam maintains that Ali ibn Abi Talib was Muhammad's designated successor.

These differing viewpoints on succession stem from varying interpretations of early Islamic history and the hadiths, which are the recorded sayings of Muhammad. Sunni Muslims contend that Muhammad did not explicitly appoint a successor, leaving the choice of leadership to the Muslim community. They recognize the legitimacy of Abu Bakr's rule, who was elected at Saqifah, as well as that of his successors, collectively known as the Rashidun caliphs.

Non-denominational Muslim (Arabic: مسلمون بلا طائفة) is a Muslim who does not belong to, does not self-identify with, or cannot be readily classified under one of the identifiable Islamic schools and branches. Such Muslims do not think of themselves as belonging to a denomination but rather as "just Muslims" or "non-denominational Muslims." Muslims who do not adhere to a sect are also known as non-sectarian Muslims.

While the majority of the population in the Middle East identify as either Sunni or Shi'a, a significant number of Muslims identify as non-denominational. According to a 2012 study by the Pew Research Center, Muslims who do not identify with a sect and identify as "just a Muslim" make up a majority of the Muslims in these countries: Kazakhstan (74%), Albania (65%), Kyrgyzstan (64%), Kosovo (58%), Indonesia (56%), Mali (55%), Bosnia and Herzegovina (54%), Uzbekistan (54%), and a plurality in four countries: Azerbaijan (45%), Russia (45%), Nigeria (42%), and Cameroon (40%). They are found primarily in Central Asia. Southeastern Europe also has a large number of Muslims who do not identify with a sect. Identification as "just a Muslim" is less prevalent in North Africa (median of 12%) and South Asia (median of 4%). In Lithuania, non-denominational Muslims fall into the category of "non-traditional religious communities", and are formally separated by law from Sunnis.

Islamic cultures or Muslim cultures refers to the historic cultural practices that developed among the various peoples living in the Muslim world. These practices, while not always religious in nature, are generally influenced by aspects of Islam, particularly due to the religion serving as an effective conduit for the inter-mingling of people from different ethnic/national backgrounds in a way that enabled their cultures to come together on the basis of a common Muslim identity. The earliest forms of Muslim culture, from the Rashidun Caliphate to the Umayyad Caliphate and early Abbasid Caliphate, was predominantly based on the existing cultural practices of the Arabs, the Byzantines, and the Persians. However, as the Islamic empires expanded rapidly, Muslim culture was further influenced and assimilated much from the Iranic, Pakistani, Bangladeshi, Indian, Caucasian, Turkic, Malay, Somali, Berber, and Indonesian cultures.

Owing to a variety of factors, there are variations in the application of Islamic beliefs in different cultures and traditions.

Twelver Shi'ism (Arabic: اِثْنَا عَشَرِيَّة, romanized: Ithnā ʿAshariyya) is the largest branch of Shia Islam, comprising about 85% of all Shia Muslims. The term Twelver refers to its adherents' belief in the twelve successors, referred to as Twelve Imams, and their belief that the last Imam, Muhammad al-Mahdi, lives in occultation (ghayba) and will reappear as "the awaited Mahdi" (al-Mahdi al-muntazar) alongside Isa al-Masih (Jesus Christ), son of Bibi Mariam (The Virgin Mary), in order to restore justice and peace.

Twelver Shi'as believe that the Twelve Imams are divinely appointed as both spiritual and political successors to the Islamic prophet Muhammad, and that they possess special knowledge and authority to guide the Muslim community. According to Twelver theology, the Twelve Imams are exemplary human individuals who rule over the Muslim community (Ummah) with justice, and are able to preserve and interpret the Islamic law (Sharia) and the esoteric meaning of the Qur'an. The words and deeds (sunnah) of Muhammad and the Imams are a guide and model for the Muslim community to follow. As a result, Muhammad and the Imams must be free from error and sin, a doctrine known as Ismah (literally 'protection') or infallibility, and must be chosen by divine decree, or nass, through Muhammad.