Habitat selection in ungulates should ensure access to abundant forage of sufficiently high quality. Species living in rugged mountain areas have to face nutritional bottlenecks regularly and should show particularly sophisticated habitat selection behaviour. However, patterns and mechanisms of such adaptations remain little studied. We analysed habitat selection and its seasonal variability of 10 GPS-collared red deer Cervus elaphus living in a topographically challenging landscape of the Swiss Alps. We hypothesised that resource selection by red deer was scale-dependent and predicted that scale-dependence would vary among seasons in relation to seasonal changes of available forage biomass and quality, which we sampled across the entire study area of 250 km². The studied population of Alpine red deer undertook altitudinal migrations and showed scale-dependent habitat selection that was strongest in winter and declined through spring and summer. Selection occurred mostly at the larger (landscape/home-range location) scale and less so at the smaller (within home-range) scale. Topographic parameters were selected mainly at the landscape scale and mostly in winter. About 70% of all instances of preference for habitat parameters were associated with above-average forage characteristics, represented mostly by higher crude protein content, in a few cases also by higher biomass or both. The overall pattern of space use by red deer characterised by migration and seasonal habitat selection was therefore closely linked to the quality of food resources, although some trade-offs with avoiding human disturbance may also have been involved.