The microclimates of the arctic tundra at Barrow, Alaska, are described for the near-surface terrestrial layers in which most biological activities take place. Temperature profiles are constructed from detailed measurements in the air, vegetation and soil, from 16 m above to 6 m below the tundra surface. Wind and radiation measurements supplement these data. Considering the tundra as a two-dimensional heat exchange surface, daily components of the heat balance are computed and summarized for a number of periods throughout the year, which are characterized by changes of the physical nature of the tundra surface such as appearance and disappearance of snow, meltwater and precipitation, and growth and decay of vegetation. Through changes in surface terrain parameters such as albedo and roughness length, and availability of water for phase changes, the thermal and moisture regimes of the near-surface layer change markedly during these periods as reflected by the heat balance.