This chapter presents the fossil and genetic evidence for an African origin and expansion of anatomically modern Homo sapiens. It provides patterns of genetic diversity among humans across the world in terms of our African origin and subsequent expansion. The chapter examines the genetic ramifications of our African origin and dispersal. Genetic data can be used to construct gene trees that show the relationships among different forms of a gene or DNA sequence. Genetic drift happens in each generation. The amount of genetic variation in a group can be measured in a number of ways. Typically, measures of genetic diversity look at the frequency of different genetic variants, such as different forms of a gene or different DNA bases. Overall, the correspondence of genetics and geography in our species reflects both the genetic legacy of serial founding in the out-of-Africa dispersal and continued interbreeding with neighboring populations.