Public health emergencies implicate difficult decisions among medical and emergency first responders about how to allocate essential resources. While various actors have proffered approaches on how to make these tough choices, meaningful guidance on shifting standards of care in major emergencies remained lacking. In March 2012, the Institute of Medicine (IOM) released additional guidance to assist facilities and practitioners to address scarce resource allocation through the development of “crisis standards of care” in catastrophes. As discussed in the article, identifying and resolving of complex practical, ethical, and legal challenges underlying real-time implementation of these standards are indispensable to protecting the public's health.