The majority, or “orthodox,” form of Islam.
Sunnis (Arab. ahl al-sunna, “people of the sunna”) are so called because they follow the sunna (customary practice), that is, the customary sayings and actions of the Prophet Muhammad. The sunna supplements the Qur’ān, clarifying points of law and theology that might otherwise be open to misinterpretation, and is derived from the hadith (report) literature, which records the words and actions of the earliest members of the Muslim umma (community).
In the early days of Islam use was made of customary practices traceable back to the Prophet, his companions, and their successors. However, in the eighth century the influential jurist al-Shāfi‘i (d. 820) insisted that the term sunna should be used to refer only to the customary practice of the Prophet (Arab. sunnat al-Nabi). In his view, this sunna of the Prophet was the second most important asl (source) of Islamic jurisprudence, after the Qur’ān, a view that despite some initial difficulties became more widely established during the ninth century.
During the period of the crusades the majority of Muslims living in the Near and Middle East, whether Arabs, Turks, or Kurds, were Sunnis. Even in Fātimid Egypt, where the rulers were Shi‘ites, the majority of the populace remained Sunnis. The Sunni community was ruled, in theory at least, by the caliph in Baghdad, or after 1261 in Cairo, but for much of the period power actually lay in the hands of the caliph’s immediate subordinates and local rulers, such as the Great Saljûq, Zangid, and Ayyûbid sultans. Few caliphs were successfully able to assert their own personal authority. In the meantime their subordinates frequently presented themselves as acting on the behalf of Islam and the caliphate.