With 940 million adherents out of about 1.1 billion Muslims, Sunni Islam is the largest Islamic sect. (Shia Muslims make up about 10% of all Muslims worldwide.) Followers of the Sunni tradition are known as Sunnis or Sunnites; they sometimes refer to themselves as Ahlus Sunnah wal-Jamaa'h, "adherents to the Sunnah and the assembly."
Sunnis have their historical roots in the majority group who followed Abu Bakr, an effective leader, as the successor of Muhammad successor instead of the prophet's cousin and son-in-law Ali. The Sunnis are so named because they believe themselves to follow the sunnah ("custom" or "tradition") of the prophet.
Some general statistics: Algeria is nearly 99% Sunni (Sunni Islam is the state religion), Kuwait is 70% and Afghanistan is 80% Sunni. Sunnis also outnumber Shiites in Israel, Egypt, Turkey, Somalia, Uzbekistan, Sudan (70%), Syria (80%), Tajikistan (85%), Libya (97%), Jordan (92%) and certain islands like the Maldives, Comoros (98%) and the Cocos (Keeling) Islands (80%).
Contrastingly, Iraq is only about 45-60% Sunni, who are concentrated mostly in the central and northern parts of the country. Sunni Muslims are a smaller minority in Iran (10%) and Bahrain (30%).
Sunnis base their religion on the Qur'an and the Sunnah as understood by the majority of the community under the structure of four schools of thought.
The four Sunni schools of law (madhahib) - the Hanafi, the Maliki, the Shafi'i and the Hanbali - are sometimes mistakenly understood as different sects, but they are not.
These four schools of religious law associate themselves with four great scholars of early Islam: Abu Haneefah, Malik, Shafi'i, and Ahmad bin Hanbal.
These scholars were known for their knowledge and piety throughout the Muslim world.
They differed only in minor issues of application of certain principles in the religion and were not in opposition to each other. In fact, Ahmad bin Hanbal was a student of Shafi'i, who was a student of Malik.
Sunnis view Shiites as from the ahlul-bidah — the people of innovation. Sunnis oppose Shi'ite beliefs concerning some of the companions of the Prophet, the belief in the Imamate and difference on the Caliphate, and others.
Other groups considered to be outside Islam by Sunnis are the Nation of Islam, Ahmadiyya, and Ismailis.