All of Sewall Wright's published papers on evolution up to 1950, and a few published later, are gathered in this volume. William Provine's introductions to each paper include pertinent references to related portions of Provine's Sewall Wright and Evolutionary Biology and Wright's four-volume masterwork, Evolution and the Genetics of Populations. By comparing the papers in this volume with the corresponding topics in the larger work, it is possible to determine the respects in which Wright extended, changed, or remained constant in his ideas over a period of sixty years. Wright's shifting-balance theory of evolution, first conceived in 1925, has proved enormously useful in modern evolutionary biology. Wright's international prestige has never been higher than it is currently, and the time is ripe for a rereading of his seminal papers. These papers are not only historically important for understanding the period of the evolutionary synthesis of the 1930s and 1940s, but continue to be stimulating and useful to working evolutionary biologists today.