In nature, several factors including ice nucleation temperature, freezing (cooling) rate, duration of exposure to ice, thawing rate and post thaw conditions contribute to the degree of injury caused by frost episodes. Our early studies demonstrated that plasma membrane ATPase is an important site of cellular response to frost and alteration in the function of this enzyme is one of the earliest manifestations of stress. We provided evidence that these alterations can be mediated by perturbation of cellular Ca and/or changes in membrane lipid composition. In potatoes, more than thirty wild species with a distinct freezing tolerance have been recognized and could be a potential source of genetic variability for the improvement of this trait. We have used these species to understand genetic control of freezing tolerance and to improve this trait in cultivated potatoes. Frost tolerance is a very complex trait with polygenic inheritance. Many factors contribute to a plant’s ability to survive a frost episode including: a) freezing tolerance in the non-acclimated state, b) capacity to cold acclimate, i.e. ability to increase freezing tolerance upon exposure to cold, c) speeds of acclimation and de-acclimation. In addition, some plant parts have the ability to survive by super cooling and avoidance of ice formation. We have demonstrated that these factors are distinct genetic components and are under independent genetic control. This implies that in order to make progress in improving freezing stress resistance, these components should be independently selected and recombined to get the desired plant. We have demonstrated that genomic dosage of the parents control the expression of frost tolerance and capacity to cold acclimate. Use of precise screening tools in these studies have allowed us, to sort genes controlling different components of frost and winter survival, to understand inheritance of  hardiness, and to make real progress in breeding hardy materials.