Muslims are the fastest-growing faith group, followed by the religiously unaffiliated, according to a new Pew Research Center study measuring the evolution of the global religious population between 2010 and 2020.

Christianity grew by 122 million members in that decade, but declined as an overall slice of the world’s population. Still, Christianity remains the world’s largest religion, with 2.3 billion believers — nearly 29% of the world’s population.