The religion of the Muslims, a monotheistic faith founded by the Prophet Muhammad in the Arabian Peninsula in the 7th century ad and is now the professed religion of nearly 1000 million people worldwide. To become a Muslim means both to accept and affirm an individual surrender to God, and to live as a member of a social community. The Muslim performs prescribed acts of worship and strives to fulfil good works within the group; the Five Pillars of Islam include profession of the faith in a prescribed form, observance of ritual prayer (five obligatory prayer sequences each day as well as non-obligatory prayers), giving alms to the poor, fasting during the month of Ramadan, and performing the pilgrimage to Mecca. These ritual observances, as well as a code governing social behaviour, were given to Muhammad as a series of revelations, codified in the Koran and supplemented by the deeds and discourse of the Prophet. Islam is regarded by its adherents as the last of the revealed religions (following Judaism and Christianity), and Muhammad is seen as the last of the Prophets, building upon and perfecting the examples and teachings of Abraham, Moses, and Jesus. Islam carries three interrelated significations: the personal individual submission to Allah; the ‘world of Islam’ as a concrete historical reality comprising a variety of communities sharing not only a common religious outlook but also a common fund of cultural legacies; and finally, the concept of an ‘ideal Muslim community’, as set forth in the Koran and supporting sources. The two main branches of Islam are the Shiites and the Sunni Muslims. Sufism is the mystical aspect of the religion that arose as a reaction to strict orthodoxy. Sufis seek personal union with God and there are many Sufi poets and scholars as well as organized orders and brotherhoods.

Islamic fundamentalism is the belief that the revitalization of Islamic society can only come about through a return to the fundamental principles and practices of early Islam. Fundamentalist movements have often been a response to political and economic decline, which is ascribed to spiritual and moral decay. In the 20th century, activist organizations, such as the Muslim Brotherhood, which was founded in Egypt in 1928 and other more radical groups, such as Hizbullah (or Hezbollah) (Party of God), became prominent. Such groups emphasize a literal interpretation of the Koran and sharia. Fundamentalists tend to stress the penal code and restrictions on women contained in the sharia, partly because such provisions have become symbols of cultural identity and opposition to westernization. Many Western observers date the resurgence in Islamic fundamentalism from the Iranian Revolution of 1979. Al-Qaeda and Islamic State are examples of contemporary terrorist groups inspired by Islamic fundamentalism.

Islamic modernism seeks to reinterpret Islam to meet the changing circumstances of contemporary life. By contrast with fundamentalism, Islamic modernism is a response to Western imperialism and economic dominance that attempts to reform legal, educational, and social structures. From the 19th century leading Muslim thinkers such as Jamal al-Din al-Afghani and his followers in Egypt, Muhammad Abduh (1849–1905) and Rashid Rida (1865–1935), were concerned at the stagnation they perceived in Muslim intellectual, political, and social life. They advocated the reform of the sharia by reopening the door of ijtihād, or reinterpretation, which orthodox Sunni Muslims have regarded as closed since the 9th century. Western scientific advances should not be rejected as incompatible with Islam, but should be integrated into the structure of a religion that is essentially scientific. Abduh distinguished between an inner unchanging core of Islamic belief and practice, and outer layers of regulations that could be varied in accordance with contemporary social practice. The Egyptian modernists’ concern with the establishment of a modern Muslim state was echoed in India, most influentially by the poet-philosopher, lawyer, and politician Muhammad Iqbal. Influenced by his study of Western philosophers such as Hegel, Fichte, and Nietzsche, Iqbal developed his own synthesis and interpretation of Islam. His view of the community as a religio-political state based on the supremacy of the sharia was influential in the establishment of Pakistan in 1947. Islamic modernism has had widespread influence in most Muslim countries, but despite its emphasis on the reform of the sharia, no systematic reform has ever been undertaken. The two main branches of Islam are Shiite and Sunni Islam. Sufism emphasises the more mystical and ascetic aspects of the religion. Ismaili Muslims, a branch of Shiite Islam, recognize seven rather than twelve imams, believing Ismail to be the last imam and to return as the Mahdi (expected one). The movement split into subgroups, including the assassins and Druzes.