This data set consists of active layer thickness (ALT) measurements based on soil temperatures in the Russian Arctic. The active layer is the top layer of ground that freezes in the winter and thaws in the summer over permafrost. Changes in ALT over northern high-latitude permafrost regions have important impacts on the surface energy balance, hydrologic cycle, carbon exchange between the atmosphere and the land surface, plant growth, and ecosystem as a whole. Warming may thicken the active layer and induce permafrost thaw. Investigators collected data from 31 ground-based stations. Derived from monthly averages, the record includes annual maximum active layer depths from 1930 to 1990. Data are in tab-delimited ASCII text format.