It has been widely acknowledged that many phenomena in ecology and evolution depend on spatial and temporal scale. However, important patterns and processes may also vary across the phylogeny and depend on phylogenetic scale. Though phylogenetic scale has been implicitly considered in some previous studies, it has never been formally conceptualized and its potential remains unexplored. Here, we develop the concept of phylogenetic scale and, building on previous work in the field, we introduce phylogenetic grain and extent, phylogenetic scaling and the domains of phylogenetic scale. We use examples from published research to demonstrate how phylogenetic scale has been considered so far and illustrate how it can inform, and possibly resolve, some of the longstanding controversies in evolutionary biology, community ecology, biogeography and macroecology. To promote the concept of phylogenetic scale empirically, we propose methodological guidelines for its treatment.