Abstract Studying adaptation to extreme climates is essential for understanding evolutionary processes and how species evolve and persist under changing environmental conditions, such as climate warming. Here, we investigate the genomic basis of adaptations in the Svalbard reindeer (Rangifer tarandus platyrhynchus), an endemic subspecies that colonized the High Arctic approximately 7,000 years ago and developed a suite of adaptations for survival under conditions of extreme cold, changes in day length, and resource scarcity. Applying scans of selection, functional analysis of coding region variation, and characterization of copy number variation across reindeer populations from Svalbard, mainland Norway, mainland Russia, and Novaya Zemlya, our comparative genomics approach identified 150 genomic regions that are differentiated in Svalbard reindeer relative to mainland reindeer (R. tarandus). These genomic regions include genes linked to fat metabolism, energy conservation, cold tolerance, body size, fur morphology, and seasonal circadian rhythm. Our study highlights the advantages of using distinct approaches to uncover the genomic basis of adaptations and provides a path for future research into the evolution of species in similar environments.