Estimates of the total number of Muslims range from 0.7 to 1.2 billion worldwide and 1.1 to 7 million in the U.S. 3 About 21% of all people on Earth follow Islam. The religion is currently in a period of rapid growth.

Christianity is currently the largest religion in the world. It is followed by about 33% of all people -- a percentage that has remained stable for decades. If current trends continue, Islam will become the most popular world religion sometime in the mid-21st century
(ISA) .