The influence of some ecological and evolutionary factors on the pattern of dental polymorphism across the geographic range of the arctic fox (Vulpes (Alopex) lagopus) was studied. Dental morphotype characters (groups of morphotypes from A to S) in 12 geographically separate populations of the arctic fox were documented. Two evolutionary trends were observed: (1) simplification of the premolars and lower carnassial (M₁), and (2) increased complexity of the upper carnassial (P⁴), third upper incisor (I₃), and third lower molar (M₃). Differences in dental morphology among arctic fox populations appear to be largely explained by evolutionary history, presence or absence of competition with the red fox (Vulpes vulpes), and diet, with a lesser influence of geography and climate. With respect to morphology, arctic foxes from the mainland populations of Eurasia and North America, are the most similar, followed by the partly-isolated island populations (Greenland, St. Lawrence Island). The most distinct forms are the arctic foxes from Commander Islands, that exist in permanent isolation.