Islam began in the seventh century CE with God’s revelations to a merchant named Muhammad, who lived in the Arabian city of Makkah. At the time, Makkah was a major commercial center, and with its rising affluence came corruption and greed. Paganism and idolatry were widespread. Muhammad himself believed in one God, and he was known for his integrity and ethical behavior. To escape the pressures and immorality of the city, Muhammad often retreated to the mountains outside Makkah to meditate. It was here, at the age of 40, that he received the first of many revelations from God through the Angel Gabriel. The revelations called upon people to believe in the one God, to help those in need, and to lead better lives. The revelations occurred over a period of 22 years, and throughout this time, Muhammad memorized each revelation and recited it back to his companions, who made written records. The written record of these revelations is the Qur`an, Islam’s holy book. The Qur`an and the Hadith—a collection of sayings and actions of the Prophet himself—have formed the basis of Islamic law from the seventh century until today.

The Arabic word Islam means “submission” to the will of God. All Muslims are regarded as equal before God in their efforts to achieve salvation through submission to God’s will. This submission is active, and requires Muslim to perform five specific duties. These are the Five Pillars of Islam: to profess belief in the One God, to pray, to give alms, to fast, and to make the pilgrimage.

As Muhammad began to proclaim his message publicly and win converts, local religious and political authorities first mocked and then persecuted him. In CE 622, persecution finally forced Muhammad to flee Makkah for the nearby city of Madinah. The next several years where characterized by a series of battles between Makkah and Madinah, from which Muhammad and his followers ultimately emerged victorious. Muhammad reentered Makkah and put an end to the worship of pagan idols in the Ka’aba—an ancient shrine believed to have been built by Abraham for the worship of the one true God. He also initiated a series of important social reforms. Regulations were established for ethical business practice, marriage and divorce, and the distribution of family inheritance. Health conditions improved through Islam’s prescribing of certain diet and hygiene practices.

The new religion spread quickly throughout the region and beyond. In less than thirty years after the Prophet Muhammad’s death, his followers had brought Islam to the Fertile Crescent, Persia, and Egypt. Within one hundred years, the Arab conquest extended to India in the east and across North Africa to Spain in the west. Many people converted to the new religion, especially in territories conquered by Muslim armies. Later, non-Muslim invaders of Muslim-controlled territories—like the Turks and Mongols of Central Asia—adopted the religion of their subjects and subsequently spread it in their homelands. Many Muslim dynasties were non-Arab, and many contributions to Islamic civilization were made by non-Arab Muslims.

For many centuries, Islamic civilization fostered cultural and scientific advances on a scale unparalleled since ancient times. Islamic scholars assimilated the ancient lore of Persia and India and the classical heritage of Greece, preserving and translating manuscripts in centers of learning as widespread as Baghdad (Iraq) and Cordoba (Spain). Not only did they preserve the legacy of Western civilization through Europe’s “Dark Ages,” but they also made significant contributions of their own in virtually every field. Islamic scholars discovered logarithms and devised the decimal system. They made original discoveries in geometry and trigonometry, and they invented algebra—itself an Arabic word.

In medicine, Muslims systematized the existing body of scientific knowledge, demonstrated circulation of the blood, developed the theory of optics, and published the first clinical account of smallpox. Two medieval Muslim physicians—Ibn Sina (Avicenna) and Ibn Rushd (Averroes)—were considered by East and West alike to be the ultimate medical authorities until modern times. Muslim interest in astronomy stemmed from the need to fix times of prayer and the direction of Makkah. Muslim astronomers developed the quadrant and astrolabe, made star charts, and were the first to use the magnetic needle in navigation. Muslim architects excelled in the technique of vaulting, and their monuments provided the inspiration for some of Europe’s Gothic cathedrals.

By the sixteenth century, Islamic civilization was among the most widespread and important civilizations on earth. Then, with the Enlightenment and Industrial Revolution, the West grew to challenge the preeminence of the Islamic world. The last of the great Islamic empires—the Turkish Ottoman Empire—finally collapsed at the end of World War I.

Allegiance to Islam as a religion remains strong. Today, more than 1 billion people throughout  the Middle East, Africa, Asia, Europe and the Americas, profess Islam. Like Christianity and Judaism, Islam is characterized by a number of sects, or branches. The most significant division is that between Sunni and Shi`a. Both agree upon the basic tenets of Islam and uphold the Five Pillars of Islam, but they differ in their conceptions of leadership and political legitimacy. The split occurred after the Prophet Muhammad’s death and reflects a disagreement over the selection of caliph, or temporal successor to Muhammad. Those that eventually became the Shi`a felt that the leader of the Islamic community should be a blood relative of the Prophet. The Sunni disagreed, arguing that Muhammad’s successor should be chosen on the basis of merit. Today, Sunni and Shi`a also differ in the nature of their religious hierarchies and in their practice of certain rituals.

There are other, much smaller religious groups that add to the diversity of the Muslim world. These include the Alawite and Druze in the Fertile Crescent—sects that began centuries ago as offshoots of Islam. All branches of Islam count Sufis, or mystics, among their adherents.

All over the world, societies are undergoing transformation more rapidly than ever before. In the process, the role of religion in public and private life is being questioned. Some promote the secularization of society. Others, alarmed at the pace and scope of change, are reemphasizing basic religious values and practices. For almost one-fifth of the world’s people, Islam remains a guide to daily living and a source of inspiration.