In Arabic, the word Islām is a verbal noun derived from the triliteral root s-l-m, which encompasses concepts of wholeness, safety, peace (salām), and submission.¹³¹⁴ In a religious context, Islam translates as the voluntary surrender or submission to the will of God, while a Muslim (the active participle of the same verb form) is one who submits.¹⁵ A closely related term from the same root, taslīm, denotes the acceptance of divine decree as well as the salutation of peace that concludes daily ritual prayers.¹⁶

Islamic theology rests upon īmān (faith), which is formally summarized in the Six Articles of Faith derived from the Quran and the Hadith of Jibril.¹⁷ The first and most fundamental article is tawḥīd, the absolute oneness and uniqueness of God. Islam teaches that Allah is the omnipotent creator, sustainer, and judge of the universe, who has no partners, offspring, or equals, thereby rejecting polytheism and the Christian doctrine of the Trinity. The second article is belief in angels, spiritual beings created from light who execute God's commands, record human deeds, and transmit revelation.

The third and fourth articles encompass belief in God's revealed books and His messengers. Muslims recognize earlier scriptures—specifically the Tawrāt (Torah) given to Moses, the Zabūr (Psalms) given to David, and the Injīl (Gospel) given to Jesus—as genuine divine revelations, though Islamic doctrine holds that these earlier texts suffered human alteration or interpolation over time. Consequently, Jews and Christians are recognized as "People of the Book". Muhammad is revered as the final prophet (khātam an-nabīyīn, or seal of the prophets), whose revelation, the Quran, restores and completes the original monotheism of Abraham.

The fifth article is belief in the Day of Judgment (Yawm ad-Dīn) and the afterlife (ākhirah), when all individuals will be bodily resurrected and held accountable for their earthly actions, resulting in eternal reward in paradise (jannah) or punishment. The sixth article is belief in divine decree (al-qadar), the principle that God possesses complete foreknowledge and sovereignty over all events, both good and bad, while humans retain moral responsibility for their choices.

The foundational text of Islam is the Quran, which Muslims believe was revealed piecemeal to Muhammad over approximately 23 years. Composed in classical Arabic, the text consists of 114 chapters (sūrahs) arranged roughly by decreasing length rather than chronological order, beginning with al-Fātiḥah (The Opener). Because the Quran is viewed as the literal speech of God, its recitation in original Arabic is central to liturgy, and scholarly exegesis (tafsīr) is used to interpret its theological, historical, and legal meanings.

Complementing the Quran is the Sunnah, the documented customs, sayings, actions, and tacit approvals of Muhammad. These traditions were transmitted orally by the Prophet's companions and later compiled into written reports known as ḥadīth. Because hadith reports vary in reliability, early Islamic scholars developed a rigorous biographical and textual science to evaluate chains of transmission (isnād) and content, categorizing collections into canonical compilations that differ between Sunni and Shia traditions.¹⁸¹⁹

Together, the Quran and the Sunnah form the primary sources of Sharīʿah, which translates as the divinely ordained path or law governing Muslim life. While Sharia represents eternal divine guidance, the human scholarly effort to interpret and apply these sources to specific circumstances is known as fiqh (jurisprudence), guided by the methodology of uṣūl al-fiqh. Jurists supplement scriptural texts with ijmāʿ (scholarly consensus) and qiyās (analogical reasoning), alongside practical principles that account for necessity (ḍarūrah), hardship (mashaqqah), and local custom (ʿurf).²⁰ Fiqh addresses both ritual worship and social relations, including family law, inheritance, commercial transactions, dietary rules, and personal ethics.

Over time, distinct methodologies crystallized into formal schools of jurisprudence (madhāhib).²¹ In Sunni Islam, four major schools endure: the Hanafi school (founded by Abu Hanifa, prominent in South and Central Asia, Turkey, and the Balkans), the Maliki school (founded by Malik ibn Anas), the Shafi'i school, and the Hanbali school.²² Shia Islam maintains its own legal traditions, most notably the Ja'fari school.

Religious observance in Islam is anchored by the Five Pillars (arkān al-Islām), which unite personal devotion with communal responsibility. The first pillar is the Shahādah, the twofold profession of faith declaring that "there is no god but Allah, and Muhammad is the messenger of Allah". Sincere recitation of the Shahadah in front of witnesses is the sole requirement for converting to Islam.

The second pillar is Ṣalāh, the ritual prayer performed five times daily facing the qiblah—the direction of the Kaaba at Masjid al-Haram in Mecca. Preceded by ritual ablution, the prayers take place at dawn (Fajr), midday (Ẓuhr), mid-afternoon (ʿAṣr), sunset (Maghrib), and nightfall (ʿIshāʾ), involving prescribed cycles of standing, bowing, and prostration while reciting Quranic verses. On Fridays, the midday prayer is replaced by a congregational service (Jumuʿah) at a mosque, accompanied by a sermon.²³

The third pillar is Zakāh, an obligatory almsgiving mandated for Muslims who possess wealth above a minimum threshold.²⁴ Designed to purify wealth and reduce social inequality, zakah is distributed to the poor, the indebted, and other vulnerable groups. The fourth pillar is Ṣawm, fasting during the ninth lunar month of Ramadan, the month in which the Quran was first revealed.²⁵ From dawn until sunset, healthy adult Muslims abstain from food, drink, and marital relations, focusing on spiritual reflection and charity.²⁶ The fifth pillar is the Ḥajj, an annual pilgrimage to Mecca during the twelfth lunar month of Dhu al-Hijjah, required once in a lifetime for every Muslim who is physically and financially able. Pilgrims perform rites commemorating Abraham, Hagar, and Ishmael, culminating in standing in prayer on the plain of Arafah.

Liturgical life follows the Hijri calendar, a lunar system of 354 or 355 days beginning with Muhammad's migration to Medina in 622 CE. Because the lunar year is roughly 10 to 11 days shorter than the solar year, Islamic observances cycle through the seasons over a 33-year period. Two major festivals (Eids) are celebrated worldwide: Eid al-Fitr (the Feast of Fast-Breaking) on the first day of Shawwal at the conclusion of Ramadan, and Eid al-Adha (the Festival of Sacrifice) on the tenth day of Dhu al-Hijjah, coinciding with the Hajj and honoring Abraham's willingness to sacrifice his son.

Islam comprises several theological and sectarian branches, the largest being Sunni and Shia Islam, which diverged following Muhammad's death over who should hold spiritual and political authority over the Muslim community. Sunni Muslims, whose name derives from Ahl as-Sunnah (People of the Tradition), constitute 85 to 90 percent of the global Muslim population, or roughly 1.7 to 1.82 billion people. Sunnis recognize the first four caliphs as legitimate successors to Muhammad and emphasize communal consensus alongside the Quran and Sunnah.

Shia Muslims represent 10 to 15 percent of Muslims worldwide, numbering between 200 and 315 million adherents. Shi'ism holds that Muhammad designated his cousin and son-in-law, Ali ibn Abi Talib, and Ali's lineal descendants (the Imams) as the divinely appointed, infallible leaders of the faith. Shia theology places strong emphasis on the spiritual authority of the Imamate as well as themes of sacrifice and martyrdom, particularly commemorating the seventh-century martyrdom of Ali's son Husayn on the day of Ashura. Between 68 and 80 percent of Shias live in Iran, Pakistan, India, and Iraq, with Shias forming the majority of the population in Iran, Iraq, Azerbaijan, and Bahrain.³⁷ Shia Islam itself is subdivided into branches, including Twelver Shi'ism (the largest group, with Usulism accounting for about 8.5 percent of all Muslims), Ismailism (roughly 18 million adherents worldwide), and Zaydism (approximately 12 million adherents, primarily in Yemen).

Smaller distinct traditions also exist. The Ibadi branch, which predates the consolidation of the main Sunni and Shia schools, accounts for 0.16 to 0.37 percent of Muslims (roughly 3 to 7 million people). Additionally, survey data from the Pew Research Center indicates that in many regions—most notably Central Asia and Southern and Eastern Europe, such as Kazakhstan (74 percent) and Albania (65 percent)—significant proportions of believers identify simply as "just a Muslim" without a specific sectarian label.

Transcending the Sunni-Shia divide is Sufism (taṣawwuf), the mystical and ascetic dimension of Islam that seeks direct personal experience of the divine. Organized into over 100 spiritual orders (ṭuruq)—such as the Chishti, Qadri, Tijaniyya, Murid, and Nimatullahi orders—Sufi practices have historically played a major role in the spread and devotional life of Islam across South Asia, Sub-Saharan Africa, and the Middle East.

With roughly two billion followers constituting about 25 percent of humanity, Islam is the majority religion in more than 50 countries. Although historically associated with the Middle East and North Africa—where more than half of the states have populations that are 95 percent Muslim or greater—only about 20 percent of the world's Muslims live in that region. Approximately 62 percent of all Muslims reside in the Asia-Pacific region. The countries with the largest Muslim populations are Indonesia (approximately 240 million), Pakistan (220 million), India (200 million, where Muslims form a minority), Bangladesh (150 million), Nigeria (110 million), Egypt (105 million), Iran (88 million), and Turkey (85 million). Roughly one-fifth of the world's Muslims live as religious minorities, including substantial populations in India, China, Russia, and Western Europe.

Demographic studies by the Pew Research Center indicate that Islam is the fastest-growing major religion globally. While religious conversion results in a modest net gain—as the number of people converting to Islam roughly equals those leaving—the primary drivers of growth are a youthful age structure and higher fertility rates, with Muslim women averaging 2.9 children globally compared to 2.2 for Christians. Projections suggest that if current demographic trends continue, the global Muslim population will surpass the Christian population in the second half of the twenty-first century.

In the twenty-first century, Muslim communities engage with diverse sociopolitical and practical developments. Islamic jurists and thinkers actively debate modern applications of Sharia and fiqh across fields such as bioethics, financial technology, gender roles, and the relationship between Islamic legal principles and secular constitutional governance. Meanwhile, the logistics of global religious observance face modern environmental pressures; during the summer Hajj of 2024, extreme temperatures in Mecca contributed to the deaths of more than 1,300 pilgrims, prompting expanded state management and digital registration systems for the pilgrimage.