The gray wolf (Canis lupus) exhibits both genetic and morphologic clinal variation across North America. Although shape variation in wolf populations has been documented, no study has been made to exhaustively quantify it, or to correlate morphologic variation with environmental variables. This study utilizes a large historical database of wolf skull linear measurements to analyze shape, and attempts to correlate it with wolf ecology. A variety of statistical tests are employed; size and shape are examined through a principal component analysis and a calculation of allometry vectors. Multiple regression analysis (both global and stepwise) are then used to test the resulting principal components against various biotic and abiotic factors. In addition, the effects of sexual dimorphism and taxonomy on morphology are explored through 1-way analysis of variance and canonical variates analysis, respectively. Several patterns are revealed, including size increase with latitude in accord with Bergmann's rule. Static allometry is significant, the fundamental pattern being a decrease in the robusticity of the basicranium relative to the viscerocranium. Sexual dimorphism, allometry, and a correlation with precipitation are other key factors driving morphological variation. Examination of these patterns has allowed us to make conclusions about the direct and indirect ways the environment has affected clinal variation in wolves.