Cryoconite holes are small cylindrical depressions which grow on the surface of ice masses worldwide. Cryoconite holes in \M McMurdo Dry Valleys of Antarctica are unique in retaining an ice lid throughout the ablation season, which isolates them from the atmosphere and the surrounding supraglacial drainage system. The holes are a refugia for life in one of the coldest and driest environments on Earth. The Dry Valleys are a nutrient poor environment, colonised by a relatively diverse microbial population that is critically dependent on glacial melt. Sources of liquid water and bioavailable nutrient are thus primary controls on the distribution of life. The biogeochemistry of the cryoconite holes is controlled by the cryoconite debris, the chemistry of the ice and any biogeochemical cycling which occurs in the holes after their formation. The cryoconite debris has variable sources and composition, but the biogeochemistry of the holes is consistent with the gradient of productivity which has been observed in Taylor Valley soils.