This edited volume applies concepts and approaches from integrative organismal biology and evolutionary biology to a songbird genus, Junco. Among the most common and abundant groups of songbirds in North America, juncos exhibit stunning phenotypic diversity across their continent-wide range, and they have been the subject of numerous foundational studies in evolution, ecology, and animal behavior for nearly a century. Across its 14 co-authored chapters, the book synthesizes past, present, and future research programs on the role of hormones in life-history trade-offs, sex differences, and the evolution of behavior, as well as research on the junco as a model of avian diversification and speciation. The 19 contributing authors are biologists from 4 countries and 13 institutes or universities who share a keen interest in the junco because of its current and historical role in understanding evolutionary processes, the mechanisms underlying social behaviors, and how animals know when to breed and migrate. All of the contributors have conducted research on the junco, and collectively they provide diverse expertise in behavioral ecology, behavioral neuroendocrinology, biogeography, bird song, conservation biology, ecological genomics, migration biology, physiological ecology, quantitative genetics, seasonality, and urban ecology. The volume is designed to appeal to scholarly audiences and serious amateurs.