The history of the Americas involved the encounter of millions of Native Americans, Europeans, and Africans. A variable admixture of these three continental groups has taken place between them throughout the continent, influenced by demography and a range of social factors. These events have had a major influence on the genetic makeup of populations across the continent. Here, we summarize the demographic history of the region, highlight some social factors that affected historical admixture, and review major patterns of diversity across the Western Hemisphere based on genetic data.2