Winter survival of Rocky Mountain Mule Deer (Odocoileus hemionus hemionus) depends on an energy conservation strategy. However, not all Mule Deer habitats are equivalent; slope, cover, weather conditions, and other factors contribute to differences in habitat use patterns and behavior among wintering populations. We studied Mule Deer on the East Front of the Rocky Mountains, Montana, and Warm Springs and Sink Creek, east-central Idaho to determine how weather and different habitats affect their winter habitat use. We located radiocollared adult female Mule Deer and collected data on weather, landscape, cover, and forage variables at locations used by deer, and at random locations during winter 2010–2011. Deer used different habitat components on the different winter ranges. On the East Front, forage, cover, and environmental conditions affected probability of deer use, and these covariates changed in magnitude depending upon weather conditions and deer behavior. In Idaho, cover and forage variables were important predictors of Mule Deer habitat use, and habitat use differed between Idaho study areas. In Warm Springs, covariates related to foraging predicted habitat use, whereas in Sink Creek covariates related to thermal or hiding cover predicted habitat use. Differences among all 3 study areas suggest that deer use different habitat components under different winter conditions. Discrepancies in habitat use among winter ranges are important when considering habitat requirements and habitat management for Mule Deer.