Shia Islam, is the second largest denomination of Islam, after Sunni Islam. The followers of Shia Islam are called Shi'as but the terms Shiites or Shi'ites are common Anglicisations. "Shia" is the short form of the historic phrase Shī‘atu ‘Alī (شيعة علي), meaning "the followers of Ali" or "the faction of Ali".
Similar to other schools of thought in Islam, Shia Islam is based on the teachings of the Islamic holy book, the Qur'an and the message of the final prophet of Islam, Muhammad. In contrast to other schools of thought, Shia Islam holds that Muhammad's family, the Ahl al-Bayt ("the People of the House"), and certain individuals among his descendants, who are known as Imams, have special spiritual and political authority over the community. Shia Muslims further believe that Ali, Muhammad's cousin and son-in-law, was the first of these Imams and was the rightful successor to Muhammad and thus reject the legitimacy of the first three caliphs.
Shias regard Ali as the most important figure after Muhammad. According to them, Muhammad suggested on various occasions during his lifetime that Ali should be the leader of Muslims after his demise. According to this view, Ali as the successor of Muhammad not only ruled over the community in justice, but also interpreted the Sharia Law and its esoteric meaning. Hence he was regarded as being free from error and sin (infallible), and appointed by God by divine decree (nass) to be the first Imam. Ali is known as "perfect man" (al-insan al-kamil) similar to Muhammad according to Shia viewpoint.
- See Wikipedia article on Shias for more information