Islam (Arabic: إسلام‎; transl.: Islām) or Islam is an Abrahamic monotheistic religion articulated by the Qur'an, a text considered to be the literal word of God (Allah, Arabic: الله ; transl.: Allāh), and by the normative teachings and example (called the sunnah, part of the hadith) of Muhammad (peace and blessings be upon him), considered to be the last prophet of God. A believer of Islam is called a Muslim.

Muslims believe that God is one and incomparable, and that the purpose of our existence is to worship him. We believe that Islam is the complete and universal version of a primordial faith that was revealed in many previous times and places, including through Abraham, Moses, and Jesus, who are also considered prophets in Islam. Muslims claim that previous messages and revelations have been partially altered or corrupted over time, but they consider the Quran (or Koran) to be an unaltered version of God's final revelation. Religious concepts and practices include the five pillars of Islam, which are basic and obligatory concepts and acts of worship, and the practice of Islamic law, which touches virtually every aspect of life and society, providing guidance on topics ranging from banking and welfare to war and the environment.

The majority of Muslims belong to one of two main denominations; with 80% to 90% being Sunni and 10% to 20% being Shia. About 13% of Muslims live in Indonesia, the largest Muslim country in the world. 25% live in South Asia, 20% in the Middle East, 2% in Central Asia, 4% in the remaining countries of Southeast Asia and 15% in sub-Saharan Africa. Significant Islamic communities are also found in China, Russia and parts of Europe. Converts and immigrant communities are found in almost every part of the world (in Portugal the latest figures put the number at around 50,000). With an estimated 1.41–1.57 billion Muslims, comprising about 21–23% of the world's population, Islam is the second largest and one of the fastest growing religions in the world. However, this figure should be taken with a grain of salt, since for obvious reasons there is no global census.