Mass critical care events are increasingly likely, yet the resource challenges to augment everyday, unrestricted critical care for a surge of disaster victims are insurmountable for nearly all communities. In light of these limitations, an expert panel defined a circumscribed set of key critical care interventions that they believed could be offered to many additional people and yet would also continue to offer substantial life-sustaining benefits for nonmoribund critically ill and injured people. They proposed Emergency Mass Critical Care, which is based on the set of key interventions and includes recommendations for necessary surge medical equipment, treatment space characteristics, and staffing competencies for mass critical care response. To date, Emergency Mass Critical Care is untested, and the real benefits of implementation remain uncertain. Nonetheless, Emergency Mass Critical Care currently remains the only comprehensive construct for mass critical care preparedness and response. This paper reviews current concepts to provide life-sustaining care for hundreds or thousands of people outside of traditional critical care sites.