Imam (/ɪˈmɑːm/, Arabic: إمام, imām; pl.: أئمة, a'immah) is an Islamic leadership position. For Sunni Muslims, Imam is most commonly used as the title of a prayer leader of a mosque. In this context, imams may lead Islamic prayers, serve as community leaders, and provide religious guidance. Thus for Sunnis, anyone can study the basic Islamic sciences and become an Imam.

For most Shia Muslims, the Imams are absolute infallible leaders of the Islamic community after the Prophet. Shias consider the term to be only applicable to the members and descendants of the Ahl al-Bayt, the family of the Islamic prophet Muhammad. In Twelver Shīʿīsm there are 14 infallibles, 12 of which are Imams, the final being Imam Mahdi who will return at the end of times.^[1] The title was also used by the Zaidi Shia Imams of Yemen, who eventually founded the Mutawakkilite Kingdom of Yemen (1918–1970).

Sunni Islam does not have imams in the same sense as the Shi'a, an important distinction often overlooked by those outside of the Islamic religion. In everyday terms, an imam for Sunni Muslims is the one who leads Islamic formal (Fard) prayers, even in locations besides the mosque, whenever prayers are done in a group of two or more with one person leading (imam) and the others following by copying his ritual actions of worship. Friday sermon is most often given by an appointed imam. All mosques have an imam to lead the (congregational) prayers, even though it may sometimes just be a member from the gathered congregation rather than an officially appointed salaried person. Women cannot be an imam in the presence of men, but allowed to be an imam to other women in the case if no man is available. The person that should be chosen, according to Hadith, is one who has most knowledge of the Quran and Sunnah (prophetic tradition) and is of good character.

In the Shi'a context, an imam is not only presented as the man of God par excellence, but as participating fully in the names, attributes, and acts that theology usually reserves for God alone.^[4] Imams have a meaning more central to belief, referring to leaders of the community. Twelver and Ismaili Shi'a believe that these imams are chosen by God to be perfect examples for the faithful and to lead all humanity in all aspects of life. They also believe that all the imams chosen are free from committing any sin, impeccability which is called ismah. These leaders must be followed since they are appointed by God.

At times, imams have held both secular and religious authority. This was the case in Oman among the Kharijite or Ibadi sects. At times, the imams were elected. At other times the position was inherited, as with the Yaruba dynasty from 1624 and 1742. See List of rulers of Oman, the Rustamid dynasty: 776–909, Nabhani dynasty: 1154–1624, the Yaruba dynasty: 1624–1742, the Al Said: 1744–present for further information.^[37] The Imamate of Futa Jallon (1727–1896) was a Fulani state in West Africa where secular power alternated between two lines of hereditary Imams, or almami.^[38] In the Zaidi Shiite sect, imams were secular as well as spiritual leaders who held power in Yemen for more than a thousand years. In 897, a Zaidi ruler, al-Hadi ila'l-Haqq Yahya, founded a line of such imams, a theocratic form of government which survived until the second half of the 20th century. (See details under Zaidiyyah, History of Yemen, Imams of Yemen.)

Ruhollah Khomeini is officially referred to as Imam in Iran. Several Iranian places and institutions are named "Imam Khomeini", including a city, an international airport, a hospital, and a university.

• Ayatollah
• Imam of Friday Prayer
• Imamate
• Mufti