The generation of heat by the human body has been likened to that of a furnace. In response to winter conditions or prolonged immersion in cold water, heat may be lost from the body more quickly than it is produced leading to hypothermia. Various factors, environmental and individual, predispose a person to hypothermia when walking on dry land or during cold water immersion. Retention of the insulating properties of the clothing worn is of crucial importance in protecting against cold injury both on land and in water. Anthropometric characteristics and behavioural and physiological responses also influence the probability of survival under these conditions. Practical recommendations for behaviour that will enhance survival during prolonged exposure to cold on land or to immersion in cold water are considered.