Developed countries like the United States are aging rapidly, and many face population stagnation or decline. This “demographic transition” leaves fewer workers to power the economy and pay into social programs, even as the number of elderly retirees increases. Immigrants make the U.S. population younger and sustain healthy population growth, giving the United States a demographic and economic advantage. Over the coming decades, the United States is projected to have faster population growth and slower aging than other developed countries. Without immigrants, the United States would lose this demographic edge. When immigrant contributions to population growth are removed, the U.S. population is projected to stop growing in the 2040s.