The Pew Research Center's Global Religious Landscape study revealed that Islam experienced the fastest growth among world religions between 2010 and 2020, with the Muslim population increasing by 347 million people—more than all other religions combined—primarily due to natural demographic growth rather than conversions.
Senior demographer Conrad Hackett explained that Muslims have higher fertility rates with an estimated 2.9 children per Muslim woman compared to 2.2 children per non-Muslim woman, along with a younger age structure that drives natural population increases, bringing Muslims to 25.6% of the global population.
While Christianity remains the world's largest religion with 2.3 billion adherents, its global share declined from 30.6% to 28.8% during the decade, with significant decreases in Europe, North America, and Australia, where the Christian population fell from 78.3% to 64% in the United States alone.
The study documented a pattern of religious disaffiliation particularly affecting Christianity, with three adults leaving the faith for every one who joined, while Islam was the only major religion where more adults converted in than left, contributing to the narrowing gap between the world's two largest religious groups.
Sub-Saharan Africa emerged as the region with the largest Christian population globally at 30.7%, surpassing Europe's 22.3%, while the religiously unaffiliated "nones" became the world's third-largest group at 24% of the global population, driven primarily by religious switching rather than demographic factors.
