During the downward trend of Quaternary global temperatures, crown-group marmots evolved to occupy harsh, seasonal environments at high latitudes and elevations. Marmots evolved hibernation and large body size, which allowed them to cope with a long, cold season with low, stressful ambient temperatures when food was unavailable. Harsh conditions during a short active season frequently cause reproductive failure and reproductive skipping in marmots. Seasonal phenology is controlled by a circannual rhythm that directs metabolic changes and fat accumulation for hibernation and reproduction. Metabolism and water balance in marmots are adapted to the low environmental temperatures of hibernation. Thus, marmots are subject to heat stress from solar radiation and high ambient temperatures during the active season. Energy conservation characterizes metabolism in marmots throughout the annual cycle: metabolic rates are lower than predicted from body size and decline during the active season, metabolism is actively suppressed to enter torpor, and most of the time during hibernation is spent at low metabolism in deep torpor. Young typically require 2 or more of the short active seasons to reach reproductive maturity and are retained at home, which leads to sociality based on kinship. Competition within the social group is expressed primarily as reproductive suppression, which delays the age of 1st reproduction that in turn strongly affects demography. Early snowmelt due to global warming may enable marmots to colonize new habitats or increase population growth. However, climate change most likely will diminish the ability of marmots to mobilize sufficient energy resources in a drier, warmer active season, which will reduce both survivorship and reproduction.