Islam is the fastest-growing religion globally, followed by the religiously unaffiliated, according to a newly released study by the Pew Research Center. The Global Religious Landscape report, which examines demographic trends from 2010 to 2020, highlights significant shifts in the global religious population.

During that decade, the Muslim population grew by 347 million, outpacing all other religious groups combined — a surge driven primarily by natural demographic growth, including higher fertility rates and a younger age structure. The religiously unaffiliated, or "nones," also saw significant growth, particularly in parts of Asia and the West.

Christianity, while still the world’s largest religion with approximately 2.3 billion adherents (nearly 29% of the global population), experienced a relative decline as a share of the world population. Despite gaining 122 million new followers, its overall growth lagged behind that of Islam and the unaffiliated.

The study, released on June 9, is the second in a series of comprehensive demographic reports by Pew, the first of which was published in 2010. It examines major world religions — including Islam, Christianity, Hinduism, Buddhism, Judaism, and the unaffiliated — as well as smaller groups such as followers of folk religions, Wiccans, Zoroastrians, and others.

“We analyze the age structure, fertility rates, education levels, and other demographic characteristics of each group,” said Conrad Hackett, senior demographer at Pew Research Center. “These factors have a direct impact on how religious populations grow or shrink over time.”

The report also considers religious switching patterns, which further shape the global religious landscape. In many countries, especially in Europe and North America, rising disaffiliation rates are reshaping the religious composition, even as natural population growth continues to drive expansion in other regions.