The threespine stickleback is a small fish of temperate coastal and fresh waters that exhibits extraordinary phenotypic diversity. Benefiting from its amenability to observation in the field and manipulation in the laboratory, Niko Tinbergen pioneered the threespine stickleback's use in behavioral studies and established it as a model system in ethology. This up-to-date volume incorporates reviews from active researchers who use studies of the fish to address a broad variety of evolutionary issues, including optimal foraging, armor variation, speciation, and the endocrine basis for correlated...