Christianity remains the world's biggest religion but is changing fast. Between 2010 and 2020, the number of Christians grew by 122 million, a 6% rise from 2.1 billion to 2.3 billion. However, the global population grew faster, and Christianity's share fell from 31% to 28.8%. Europe and North America saw big drops in Christians. Europe’s Christian population fell by 9% to 505 million. North America’s numbers fell 11% to 238 million. In contrast, sub-Saharan Africa saw a sharp rise of 31%, reaching 697 million Christians. By 2020, 31% of Christians lived in sub-Saharan Africa, up from earlier decades, while Europe’s share dropped to 22%. The share of Christians in populations dropped significantly in North America (down 14 points) and Europe (down 8 points). In countries like the United Kingdom (49%), Australia (47%), France (46%), and Uruguay (44%), Christians lost majority status as non-religious groups grew. Religious switching plays a major role. For every person joining Christianity, 3.1 leave it, often becoming religiously unaffiliated. Globally, more people are leaving religion than joining it, especially among adults aged 18–54. Fertility rates are still important, but switching reduces Christian growth. Muslims mainly grow through higher birth rates and youth. By 2020, the world’s religious makeup was: Christianity 28.8%, Muslims 25.6%, religiously unaffiliated 24.2%, Hindus 14.9%, and Buddhists 4.1%. Christianity is shifting toward the Global South, with Africa rising as Europe and North America decline.