In recent decades, Muslims have become a small but significant minority in most Western countries. Taken as a group, these nations have an aggregate Muslim population that is probably between 1 and 4 percent. These populations are often concentrated geographically, and this figure can be much higher for specific countries or localities. Exact figures can be difficult to come by: Some researchers define Muslims narrowly, in terms of those adherents who regularly attend mosques; others consider Muslims in terms of broader cultural groupings. In some countries, like France, it is discouraged or even illegal to acquire official government statistics based on religion. Finally, estimates can be influenced by religious and political agendas.

Nonetheless, a variety of research methods using surveys, numbers of mosques and immigration records, can provide fairly reliable data. Counts of Muslim populations in the United States, for example, range from less than one million to over ten million, though figures clustering around either 2-3 million or 6-7 million are most often cited. The number provided here, roughly 4 million, given by demographer David Barrett, is widely considered to be reliable, and is the source for several reference texts, including the Encyclopedia Britannica.

Sources: David B. Barrett & Todd M. Johnson of the Intl. Bulletin of Missionary Research; GUARDIAN, “Special Report: Muslim Britain”; CHRISTIAN RESEARCH JOURNAL, “Islam Grows Into a Strong Presence in America” by Joseph P. Gudel; IINA: International Islamic News Agency, from Lexis Academic; MANCHESTER GUARDIAN, “Spain Uneasy as Number of Muslim Migrants Grows”; A GUIDEBOOK ON ISLAM AND MUSLIMS IN THE WIDE CONTEMPORARY EUROPE by B. Maréchal; Swedish Institute; TURKISH DAILY NEWS, “Immigrant Muslims In Germany and Within the E.U.”