From the Pew Research Center.

A comprehensive demographic study of more than 200 countries finds that there are 1.57 billion Muslims of all ages living in the world today, representing 23% of an estimated 2009 world population of 6.8 billion.

While Muslims are found on all five inhabited continents, more than 60% of the global Muslim population is in Asia and about 20% is in the Middle East and North Africa. However, the Middle East-North Africa region has the highest percentage of Muslim-majority countries. Indeed, more than half of the 20 countries and territories1 in that region have populations that are approximately 95% Muslim or greater.