Almost 30 y ago, the field of intraspecific phylogeography laid the foundation for spatially explicit and genealogically informed studies of population divergence. With new methods and markers, the focus in phylogeography shifted to previously unrecognized geographic genetic variation, thus reducing the attention paid to phenotypic variation in those same diverging lineages. Although phenotypic differences among lineages once provided the main data for studies of evolutionary change, the mechanisms shaping phenotypic differentiation and their integration with intraspecific genetic structure have been underexplored in phylogeographic studies. However, phenotypes are targets of selection and play important roles in species performance, recognition, and diversification. Here, we focus on three questions. First, how can phenotypes elucidate mechanisms underlying concordant or idiosyncratic responses of vertebrate species evolving in shared landscapes? Second, what mechanisms underlie the concordance or discordance of phenotypic and phylogeographic differentiation? Third, how can phylogeography contribute to our understanding of functional phenotypic evolution? We demonstrate that the integration of phenotypic data extends the reach of phylogeography to explain the origin and maintenance of biodiversity. Finally, we stress the importance of natural history collections as sources of high-quality phenotypic data that span temporal and spatial axes.phylogeography | phenotype | function | trait | concordance P hylogeography, as originally defined, focused on processes governing the spatial distribution of genealogical lineages within species (1). One of the strengths of the field at its inception was formalizing conceptual links among heredity (processes at the level of individual pedigrees), divergence at the population level, and phylogenetic relationships among species (1). This analytical framework bridged microevolutionary processes acting within populations and macroevolutionary patterns at larger spatial and temporal scales. From the earliest applications, empirical phylogeographic studies described spatial patterns of genetic diversity and inferred underlying mechanisms, thus contributing to the explanatory and predictive power of the field (2). If most species show phylogeographic structure caused by landscape features that impede gene flow, then the geographic distribution of divergent lineages should coincide among species that coinhabit those landscapes. Further, phylogeographic breaks or contact zones should arise as lineages diverge allopatrically or come into secondary contact after divergence, respectively. This explicit prediction (1) resulted in a search for shared geographic patterns in genetic structure among species and the birth of comparative phylogeography (3, 4). Now, with thousands of taxon-specific phylogeographic studies published and synthesized in comparative studies (5, 6), we have learned a tremendous amount about the geography of genetic structure both within and among species.Phylogeogra...