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. More than 300 million Muslims, or one-fifth of the world’s Muslim population, live in countries where Islam is not the majority religion. These minority Muslim populations are often quite large. India, for example, has the third-largest population of Muslims worldwide. China has more Muslims than Syria, while Russia is home to more Muslims than Jordan and Libya combined. Of the total Muslim population, 10-13% are Shia Muslims and 87-90% are Sunni Muslims. Most Shias (between 68% and 80%) live in just four countries: Iran, Pakistan, India and Iraq. These are some of the key findings of Mapping the Global Muslim Population: A Report on the Size and Distribution of the World’s Muslim Population, a new study by the Pew Research Center’s Forum on Religion & Public Life. The report offers the most up-to-date and fully sourced estimates of the size and distribution of the worldwide Muslim population, including sectarian identity. Previously published estimates of the size of the global Muslim population have ranged widely, from 1 billion to 1.8 billion.2 But these commonly quoted estimates often have appeared without citations to specific sources or explanations of how the figures were generated. The Pew Forum report is based on the best available data for 232 countries and territories. Pew Forum researchers, in consultation with nearly 50 demographers and social scientists at universities and research centers around the world, acquired and analyzed about 1,500 sources, including census reports, demographic studies and general population surveys, to arrive at these figures – the largest project of its kind to date. (See Methodology for more detail.)