Scaling refers to the structural and functional consequences of differences in size (or scale) among organisms of more or less similar design. Investigations into such size-related phenomena in primates continue to be a primary concern of physical anthropologists, primatologists, and other vertebrate biologists. An overview of allometric studies, especially those of the last decade or so, documents the enormous impact of body size variation in primates for interpretations of comparative behavior and ecology, morphology and physiology, and evolutionary biology. Specific methodological issues are also discussed (the utility of the bivariate power function, regression models, and choice of body size variables). Distinctions are drawn between ontogenetic and static adult forms of intraspecific allometry, and the genetic assumptions about extrapolation of either type to evolutionary allometry are briefly reviewed. Ontogenetic allometries of the locomotor skeleton in African apes are used to illustrate the potential utility and limitations of this approach for our understanding of evolutionary mechanisms. Selected aspects of locomotor adaptation in primates are also explored through interspecific allometric analysis: an analysis of long bone size and shape with respect to competing biomechanical theories of functional equivalence; scaling of interlimb proportions and functional competence in climbing; and relative limb proportions and the reconstruction of locomotion and posture in fossil “hominoids”.