As a base for future scientific investigations and their application to practical human needs, some small mammal bioclimate studies are made of northern regions. Two major divisions are established - the tundra (arctic treeless region) and the taiga (subarctic spruce forest). Further subdivisions are made, and ten representative study areas are selected for Alaska. Some winter bioclimatic conditions - such as the snow cover and the moss layer - of taiga small mammals are analyzed. Points of potential value to the Air Force are drawn from studies on the importance of topographical irregularities in the formation of suitable microhabitats. Definitions of biological and ecological terms are appended.