Religious groups

In the 20th century study of comparative religion, major religious groups or "world religions" were divided up by adherence to a specific philosophy or theology. However, there is no consensus among researchers as to the best methodology for determining the religiosity profile of the world's population. A number of fundamental aspects are unresolved:


 * Whether to count "historically predominant religious culture[s]"
 * Whether to count only those who actively "practice" a particular religion
 * Whether to count based on a concept of "adherence"
 * Whether to count only those who expressly self-identify with a particular denomination
 * Whether to count only adults, or to include children as well
 * Whether to rely only on official government-provided statistics
 * Whether to use multiple sources and ranges or single "best source[s]"

Nonetheless, Christianity, Islam, Hinduism, and Buddhism are usually considered the respective top four.

By world population
The table below lists religions classified by philosophy; however, religious philosophy is not always the determining factor in local practice. Please note that this table includes heterodox movements as adherents to their larger philosophical category, although this may be disputed by others within that category. For example, Cao Đài is listed because it claims to be a separate category from Buddhism, while Hoa Hao is not, even though they are similar new religious movements.

The population numbers below are computed by a combination of census reports, random surveys (in countries where religion data is not collected in census, for example USA or France), and self-reported attendance numbers, but results can vary widely depending on the way questions are phrased, the definitions of religion used and the bias of the agencies or organizations conducting the survey. Informal or unorganized religions are especially difficult to count. Some organizations may wildly inflate their numbers.

By region

 * Religion in Africa
 * Religion in Asia
 * Religion in India
 * Religion in China
 * Muslim world (SW Asia and N Africa)
 * Religion in North America
 * Religion in Canada
 * Religion in Mexico
 * Religion in the United States
 * Religion in South America
 * Religion in Australia
 * Religion in Europe
 * Religion in the European Union

Trends in adherence


Since the late 19th century the demographics of religion have changed a great deal. Some countries with a historically large Christian population have experienced a significant decline in the numbers of professed active Christians. Symptoms of the decline in active participation in Christian religious life include declining recruitment for the priesthood and monastic life, as well as diminishing attendance at church. At the same time, there has been an increase in the number of people who identify themselves as secular humanists. In many countries, such as the People's Republic of China, communist governments have discouraged religion, making it difficult to count the actual number of believers. However, after the collapse of communism in numerous countries of Eastern Europe and the former Soviet Union, religious life has been experiencing resurgence there, particularly in the forms of Neopaganism and Far Eastern religions.

Following is some available data based on the work of World Christian Database and its predecessor, the World Christian Encyclopedia:

While controversial in some respects, the results have been studied and found "highly correlated with other sources of data" but "consistently gave a higher estimate for percent Christian in comparison to other cross-national data sets" according to one study.

A 2002 Pew Research Center study found that, generally, poorer nations had a larger proportion of citizens who found religion to be very important than richer nations, with the exception of the United States.