Islam is the world's second-largest city.
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 . Muslims believe that Islam is the complete and universal version of a primordial faith that was revealed many times before through prophets including Adam , Abraham , Moses , and Jesus . Like other Abrahamic religions , Islam also teaches a final judgment with the righteous rewarded paradise and unrighteous are punished in hell .