Islam has many followers.
Islam . It is the world 's second-largest religion and the fastest-growing major religion in the world , with over 1.8 billion followers or 24.1 % of the global population , known as Muslims . Most Muslims are of one of two denominations : Sunni ( 75 -- 90 % ) or Shia ( 10 -- 20 % ) . About 13 % of Muslims live in Indonesia , the largest Muslim-majority country , 31 % in South Asia , the largest population of Muslims in the world , 23 % in the Middle East-North Africa , where it is the dominant religion , and 15 % in Sub-Saharan Africa .