BACKGROUND: Significant legal challenges arise when health-care resources become scarce and population-based approaches to care are implemented during severe disasters and pandemics. Recent emergencies highlight the serious legal, economic, and health impacts that can be associated with responding in austere conditions and the critical importance of comprehensive, collaborative health response system planning. This article discusses legal suggestions developed by the American College of Chest Physicians (CHEST) Task Force for Mass Critical Care to support planning and response efforts for mass casualty incidents involving critically ill or injured patients. The suggestions in this chapter are important for all of those involved in a pandemic or disaster with multiple critically ill or injured patients, including front-line clinicians, hospital administrators, and public health or government officials. METHODS: Following the CHEST Guidelines Oversight Committee's methodology, the Legal Panel developed 35 key questions for which specific literature searches were then conducted. The literature in this field is not suitable to provide support for evidence-based recommendations. Therefore, the panel developed expert opinion-based suggestions using a modified Delphi process resulting in seven final suggestions. RESULTS: Acceptance is widespread for the health-care community's duty to appropriately plan for and respond to severe disasters and pandemics. Hospitals, public health entities, and clinicians have an obligation to develop comprehensive, vetted plans for mass casualty incidents involving critically ill or injured patients. Such plans should address processes for evacuation and limited appeals and reviews of care decisions. To legitimize responses, deter independent actions, and trigger liability protections, mass critical care (MCC) plans should be formally activated when facilities and practitioners shift to providing MCC. Adherence to official MCC plans should contribute to protecting hospitals and practitioners who act in good faith from liability. Finally, to address anticipated staffing shortages during severe and prolonged disasters and pandemics, governments should develop approaches to formally expand the availability of qualified health-care workers, such as through using official foreign medical teams. CONCLUSIONS: As a fundamental element of health-care and public health emergency planning and preparedness, the law underlies critical aspects of disaster and pandemic responses. Effective responses require comprehensive advance planning efforts that include assessments of complex legal issues and authorities. Recent disasters have shown that although law is a critical response tool, it can also be used to hold health-care stakeholders who fail to appropriately plan for or respond to disasters and pandemics accountable for resulting patient or staff harm. Claims of liability from harms allegedly suffered during disasters and pandemics cannot be avoided altogether. However, appropriate planning and legal protections can help facilitate sound, consistent decision-making and support response participation among health-care entities and practitioners.