Principles of Population Genetics, Fourth Edition, is a thoroughly updated introduction to the field that is at last ascending to its rightful position of centrality to evolutionary genomics and human genetics. Rapid and inexpensive genotyping and sequencing have produced a profusion of data on genetic variation, along with a pressing need to inform students from many fields about the models that describe the underlying processes that give rise to observed patterns of genetic variation. This book provides a balanced presentation of theory and observation for students at the undergraduate and graduate levels as well as newcomers from fields like human genetics.