Believe that Islamic leadership must come through the Prophet's bloodline. They support Ali, Muhammad's cousin and son-in-law as the legitimate successor.

Their supreme leader was killed in 680 by the ruling rival sect. They value martyrdom and sacrifice.

Believe that Islam should be led by the most qualified individual. They elected Abu Bakr, a friend of Muhammad and the father of his wife Aisha, as his successor.

They are the majority in Iran, Iraq and Bahrain, and have endured a long history of marginalization in the Arab world.

They are 85% of the world's 1.6 billion Muslims. They are the majority in Saudi Arabia, Turkey, Pakistan, India, Bangladesh, Malaysia and Indonesia.

Karbala, Kufa and Najaf in Iraq are considered as revered shrines.

Ousted Iraqi Dictator Saddam Hussein is a member of this sect.

Perform pilgrimage to Mecca, the holy shrine, and regard the Koran as holy book.

Believe that the 12th and final imam is hidden and will return one day as Mahdi or Messiah to fulfill divine will.

Fast during the holy month of Ramadan.

Their members include ISIS and Osama Bin Laden.

Islamic authority is based more on the Koran and the traditions of Mohammed compared to religious scholars.

Include the Alawite sect of Syrian President Bashar al-Assad.

Give great authority to their ayatollahs, or high-ranking Muslim scholars, who are seen as God's guides.

Believe Allah is the only God and Muhammad his messenger.