Shia is the second major religion in Islam. The word Shi'a is a short form of 'Shi'a' Ali, the follower or party of Ali bin Abi Talib, the first Imam. Shiites make up between 5% and 5% of the total Muslim population of the world and 5% of the Middle East Muslim population.Although it has been divided into several branches throughout Shiite history, today there are only three main categories of twelve Shiites, Ismaili Shiites and Zaidi Shiites. The Shiite religion is based on an interpretation of the Qur'an and the Sunnah of the Prophet (PBUH), which has been expressed and taught by the Shiite Imams.The common denominator of all Shiites is the belief in the appointment of Ali ibn Abi Talib for the succession of Muhammad, the Prophet of Islam, and his Imamate after him. The Shiites believe that it is God alone who can install a person to preserve Islam, teach the Shari'a, and lead the ummah as an imam.