Wilderness emergency medical services (WEMS) systems have components and requirements that are different from those of traditional EMS systems. These differences arise from the extremes of time and environmental exposure and the limited available resources that help define the wilderness environment. Although disaster systems combine wilderness and traditional EMS system components, most WEMS systems have had to develop independently on a localized level and in response to the need of a particular community or location. In many cases, volunteers provide much of the personnel and resources available to law enforcement agencies that are ultimately tasked with the responsibility of oversight for effecting rescues in a wilderness setting.