Critical care medicine is a relatively young specialty that was developed in response to potentially reversible life-threatening illness and was facilitated by developments such as new drugs, support equipment, and monitoring technology. It has been largely practiced within the four walls of an intensive care unit (ICU). However, now there are increasing numbers of critically ill and at-risk patients in acute hospitals who are suffering potentially preventable, serious complications that may result in death because of a lack of appropriate systems, skills, and expertise outside of the ICU. Critical care specialists are expanding their roles beyond the four walls of their ICUs and becoming involved with strategies such as the medical emergency team, a concept designed to recognize critical illness early and to respond rapidly to resuscitate patients wherever they are in the hospital.