Islam is an Abrahamic monotheistic religion centred primarily around the Quran, a religious text considered by Muslims to be the direct word of God as it was revealed to Muhammad, the main and final Islamic prophet. It is the world's second-largest religion behind Christianity, with its followers ranging between 1-1.8 billion globally, or around a quarter of the world's population. Due to the average younger age and higher fertility rate, Islam is the world's fastest growing major religious group, and is projected by Pew Research Center to be the world's largest religion by the end of the 21st century, surpassing that of Christianity. It teaches that God is merciful, all-powerful, and unique, and has guided humanity through various prophets, revealed scriptures, and natural signs, with the Quran serving as the final and universal revelation and Muhammad serving as the "Seal of the Prophets" . The teachings and practices of Muhammad documented in traditional collected accounts provide a secondary constitutional model for Muslims to follow after the Quran.
Muslims believe that Islam is the complete and universal version of a primordial faith that was revealed many times through earlier prophets such as Adam, Noah, Abraham, Moses, and Jesus, among others; these earlier revelations are attributed to Judaism and Christianity, which are regarded in Islam as spiritual predecessor faiths. They also consider the Quran, when preserved in Classical Arabic, to be the unaltered and final revelation of God to humanity. Like other Abrahamic religions, Islam also teaches of a "Final Judgement" wherein the righteous will be rewarded in paradise (Jannah) and the unrighteous will be punished in hell (Jahannam). The religious concepts and practices of Islam include the Five Pillars of Islam—considered obligatory acts of worship —and following Islamic law, sharia, which touches on virtually every aspect of life, from banking and finance and welfare to women's roles and the environment. The Five Pillars comprise Shahada, the Islamic oath and creed; Salah, daily prayers; Zakat, forms of almsgiving; Sawm, religious fasting; and Hajj, a mandated once-in-a-lifetime pilgrimage to Mecca during the 12th month of the lunar calendar. Khitan, the religious rite of circumcision, is seen as obligatory or recommendable for male followers. Prominent religious festivals include Ramadan, Eid al-Fitr, and Eid al-Adha. The cities of Mecca, Medina, and Jerusalem are home to the three holiest sites in Islam, in descending order: Masjid al-Haram, Al-Masjid an-Nabawi, and Al-Aqsa Mosque, respectively.
Islam originated in the 7th century at Jabal al-Nour, a mountain peak near Mecca where Muhammad's first revelation is said to have taken place. Through various caliphates, the religion later spread outside of Arabia shortly after Muhammad's death, and by the 8th century, the Umayyad Caliphate had imposed Islamic rule from the Iberian Peninsula in the west to the Indus Valley in the east. The Islamic Golden Age refers to the period traditionally dated from the 8th century to the 13th century, during the reign of the Abbasid Caliphate, when much of the Muslim world was experiencing a scientific, economic, and cultural flourishing. The expansion of the Muslim world involved various states and caliphates as well as extensive trade and religious conversion as a result of Islamic missionary activities (dawah).
There are two major Islamic denominations: Sunni Islam (85–90 percent) and Shia Islam (10–15 percent); combined, they make up a majority of the population in 49 countries. While Sunni–Shia differences initially arose from disagreements over the succession to Muhammad, they grew to cover a broader dimension both theologically and juridically, with the divergence acquiring notable political significance. Approximately 12 percent of the world's Muslims live in Indonesia, the most populous Muslim-majority country; 31 percent live in South Asia; 20 percent live in the Middle East–North Africa; and 15 percent live in sub-Saharan Africa. Sizable Muslim communities are also present in the Americas, China, and Europe.