Species spatial turnover, or β-diversity, induces a decay of community similarity with geographic distance known as the distance-decay relationship. Although this relationship is central to biodiversity and biogeography, its theoretical underpinnings remain poorly understood. Here, we develop a general framework to describe how the distance-decay relationship is influenced by population aggregation and the landscape-scale species-abundance distribution. We utilize this general framework and data from three tropical forests to show that rare species have a weak influence on distance-decay curves, and that overall similarity and rates of decay are primarily influenced by species abundances and population aggregation respectively. We illustrate the utility of the framework by deriving an exact analytical expression of the distance-decay relationship when population aggregation is characterized by the Poisson Cluster Process. Our study provides a foundation for understanding the distance-decay relationship, and for predicting and testing patterns of beta-diversity under competing theories in ecology.