Permafrost, or materials with temperature at 0°C for at least two consecutive years, underlies most Arctic areas as a continuous substrate, but becomes discontinuous in the subarctic. The permafrost region also abounds in ground ice. Large ice bodies may be found with ice wedge polygons, pingos, paisas and massive ice of several possible origins. Precautionary measures such as the avoidance of ice-rich areas should be considered while engineering techniques have been developed to minimise permafrost disturbance and to reduce damages to the artificial structures. Permafrost hydrology studies the distribution, movement and storage of water as is directly or indirectly influenced by the presence of perennially frozen ground. Pertinent to freeze-thaw considerations are the presence of water in the medium and the thermal properties of the medium, be it bedrock, soil materials or ice. Suprapermafrost groundwater and soil moisture in the active layer are subject to freezing in winter.