This study examines how the distribution and abundance of prey species influenced arctic fox Alopex lagopus diet on Svalbard during the summers of 1997, 1998 and 1999. The arctic fox together with the glaucous gull Larus hyperboreus are the only predators of this terrestrial ecosystem, and during summer the potential prey are confined to a few prey species such as various colonial seabirds, geese and Svalbard reindeer Rangifer tarandus platyrhynchus. There is great variation in distribution of prey over short distances, resulting in highly contrasting patterns in terms of both prey abundance and availability. Arctic fox diet was investigated by collecting scats (N = 818) at dens used for breeding. A cluster analysis based on similarities in the contents of scats revealed that arctic fox habitat could be divided into three distinct prey resource landscapes: two inland areas dominated by the prey species 'reindeer' and 'reindeer and geese', respectively, and one coastal resource area dominated by 'seabirds'. The occurrence of reindeer, geese and seabirds in the scats varied significantly among these resource landscapes. Svalbard reindeer, seabirds belonging to Alcidae and Procellariidae and geese belonging to Anseridae were the dominant prey species; volume percentages in the scats were 33, 33 and 15%, respectively. Svalbard rock ptarmigan Lagopus mutus hyperboreus, eggs, waders, snow buntings Plectrophenax nivalis and vegetation also occurred in minor proportions of the scats. The arctic fox showed a functional response to changes in prey availability. There was a positive correlation between the availability of these main prey species and their occurrence in the scats. Whenever available, arctic foxes preferred geese to seabirds and reindeer, and seabirds to reindeer. The arctic foxes in our study were opportunistic feeders, varying their food habits with prey availability.