As of 2010, there were 1.1 billion religiously unaffiliated people around the world, accounting for about one-in-six (16%) people worldwide. This makes the unaffiliated the third-largest religious grouping worldwide, behind Christians and Muslims, and about equal in size to the world's Catholic population. During the next few decades, the number of religiously unaffiliated people around the world is projected to grow modestly, rising to a peak of more than 1.2 billion in 2040 and then dropping back slightly.

The religiously unaffiliated are heavily concentrated in the Asia-Pacific region, where 76% resided in 2010 and 68% are projected to reside in 2050. The share of the unaffiliated population residing in Europe is projected to grow from 12% in 2010 to 13% in 2050. North America, which had about 5% of the world’s unaffiliated population in 2010, is expected to have 9% in 2050. The shares of the unaffiliated living in the three other regions are expected to increase modestly but remain relatively small. 

The religiously unaffiliated population includes atheists, agnostics and people who do not identify with any particular religion. However, many of the religiously unaffiliated do hold some religious or spiritual beliefs. For example, surveys have found that belief in God or a higher power is shared by 7% of unaffiliated Chinese adults, 30% of unaffiliated French adults and 68% of unaffiliated U.S. adults.  

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