Islam is the world's second-largest religion, with approximately 1.9 billion adherents spread across every continent, though with its greatest concentrations in South and Southeast Asia, the Middle East, and sub-Saharan Africa. The word Islam is an Arabic noun meaning "submission" or "surrender" — specifically, submission to the will of God (Allah, from Arabic al-ilah, "the God"). A person who submits is a Muslim. Islam understands itself not as a new religion but as the restoration and final perfection of the monotheism first revealed to Abraham — the same divine truth of which Judaism and Christianity are earlier, partial expressions.
The Prophet Muhammad
Islam was established through the prophethood of Muhammad ibn Abdullah, born around 570 CE in Mecca, in the Arabian Peninsula. An orphan raised by his grandfather and then his uncle, Muhammad worked as a merchant and became known in Mecca for his trustworthiness and integrity — earning the epithet al-Amin, "the trustworthy." Around 610 CE, at approximately forty years of age, while on a spiritual retreat in the cave of Hira on Mount Jabal al-Nour near Mecca, he received the first of what would become a sustained series of revelations over twenty-three years. The revelations came, according to Islamic tradition, through the Angel Gabriel (Jibril), who commanded him to recite. These revelations, memorised by his followers and partially recorded during his lifetime, constitute the Quran.
Muhammad initially preached his message privately in Mecca, then publicly, attracting both followers and determined opposition from the Meccan establishment, whose political and economic power was bound up with the polytheistic religious system centred on the Kaaba shrine. Persecution drove the nascent Muslim community to migrate in 622 CE to Medina — the Hijra, or emigration, which marks the beginning of the Islamic calendar. In Medina, Muhammad became not only a spiritual leader but a political and military one, eventually returning to Mecca in 630 CE at the head of a large force and establishing Islam as the dominant religion of the peninsula. He died in 632 CE, having transmitted a revelation understood by his community as the final and complete word of God to humanity.
The Quran
The Quran (al-Qur'an — "the Recitation") is Islam's central scripture and the primary source of Islamic theology, law, and ethics. It is understood by Muslims to be the verbatim word of God as dictated to Muhammad through Gabriel — not Muhammad's own composition or interpretation, but divine speech in human language. This understanding of the Quran as directly divine distinguishes it from the scriptural status accorded to the Bible in Christian theology, where the human authors of scripture are understood as inspired but not simply dictated to.
The Quran is organised into 114 suras (chapters), which vary greatly in length and are arranged roughly in order of decreasing length rather than chronologically. Each sura consists of ayat (verses, literally "signs"). The longer suras were generally revealed during the Medinan period of Muhammad's ministry, when the concerns of governance and community law were pressing; the shorter suras, many of them among the most poetically powerful, tend to be earlier Meccan revelations focused on the nature of God, the coming Day of Judgment, and the fate of those who disbelieve.
The Quran is not merely scripture to be read but to be recited — its Arabic text is considered of divine perfection, and the memorisation of the entire Quran (the achievement of a hafiz) is held in the highest esteem. Muslims who have memorised the Quran are estimated to number in the millions worldwide.
Hadith and the Sunnah
Alongside the Quran, Islamic religious life and law are governed by the Sunnah — the practice and example of the Prophet Muhammad as recorded in the Hadith literature. The Hadith are reports (hadiths) of what Muhammad said, did, or tacitly approved, as transmitted by chains of narrators (isnad) going back to his companions. The scholarly discipline of Hadith criticism — assessing the reliability of transmitter chains and the soundness of individual reports — became one of the most sophisticated philological enterprises of the medieval world.
The most authoritative Hadith collection in Sunni Islam is Sahih Bukhari, compiled by the scholar Muhammad al-Bukhari (810–870 CE), who lived two centuries after the Prophet. Bukhari is said to have examined 600,000 hadiths and accepted approximately 7,275 as rigorously verified (sahih, "sound"). Each report was checked for compatibility with the Quran and for the veracity of its chain of narrators. Bukhari's collection, together with that of his contemporary Muslim ibn al-Hajjaj (Sahih Muslim), is recognised by the overwhelming majority of the Sunni Muslim world as the most authoritative compilation of prophetic traditions. The Shia hadith tradition draws on a different body of narrators, centred on the family of the Prophet (the ahl al-bayt).
The Five Pillars of Islam
The Five Pillars are the foundational religious duties that define Muslim practice across all traditions:
- Shahada — the declaration of faith: "There is no god but God, and Muhammad is the messenger of God."
- Salat — ritual prayer performed five times daily, facing Mecca, in Arabic
- Zakat — obligatory almsgiving, calculated as a proportion of one's wealth, distributed to the poor
- Sawm — fasting from dawn to sunset throughout the month of Ramadan
- Hajj — pilgrimage to Mecca, obligatory once in a lifetime for those with the physical and financial means
Major Traditions and Schools of Law
The two principal branches of Islam are Sunni (approximately 85–90% of Muslims worldwide) and Shia (approximately 10–15%). The division arose from the question of legitimate succession after Muhammad's death — Sunni Islam recognised the first four caliphs (Abu Bakr, Umar, Uthman, and Ali), while Shia Islam holds that leadership should have passed exclusively through the family of the Prophet, beginning with Ali ibn Abi Talib. Within Sunni Islam, four main schools of Islamic law (madhabs) are recognised: Hanafi, Maliki, Shafi'i, and Hanbali, each representing a distinct methodology of legal reasoning from the Quran and Sunnah.
For authoritative scholarly reference, see the Encyclopaedia Britannica entry on Islam. Primary texts in translation are available at sacred-texts.com's Islam section. The Wikipedia article on Islam provides comprehensive further reading. For philosophical aspects of Islamic thought, the Stanford Encyclopedia of Philosophy's entry on Islamic philosophy is authoritative.
On this site: Judaism and Christianity are the two Abrahamic traditions with which Islam stands in closest theological relationship.