In the United States, injury is the leading cause of death for persons aged 1-44 years. In 2008, approximately 30 million injuries were serious enough to require the injured person to visit a hospital emergency department (ED); 5.4 million (18%) of these injured patients were transported by Emergency Medical Services (EMS). On arrival at the scene of an injury, the EMS provider must determine the severity of injury, initiate management of the patient's injuries, and decide the most appropriate destination hospital for the individual patient. These destination decisions are made through a process known as "field triage," which involves an assessment not only of the physiology and anatomy of injury but also of the mechanism of the injury and special patient and system considerations. Since 1986, the American College of Surgeons Committee on Trauma (ACS-COT) has provided guidance for the field triage process through its "Field Triage Decision Scheme." This guidance was updated with each version of the decision scheme (published in 1986, 1990, 1993, and 1999). In 2005, CDC, with financial support from the National Highway Traffic Safety Administration, collaborated with ACS-COT to convene the initial meetings of the National Expert Panel on Field Triage (the Panel) to revise the decision scheme; the revised version was published in 2006 by ACS-COT (American College of Surgeons. Resources for the optimal care of the injured patient: 2006. Chicago, IL: American College of Surgeons; 2006). In 2009, CDC published a detailed description of the scientific rationale for revising the field triage criteria (CDC. Guidelines for field triage of injured patients: recommendations of the National Expert Panel on Field Triage. MMWR 2009;58[No. RR-1]). In 2011, CDC reconvened the Panel to review the 2006 Guidelines in the context of recently published literature, assess the experiences of states and local communities working to implement the Guidelines, and recommend any needed changes or modifications to the Guidelines. This report describes the dissemination and impact of the 2006 Guidelines; outlines the methodology used by the Panel for its 2011 review; explains the revisions and modifications to the physiologic, anatomic, mechanism-of-injury, and special considerations criteria; updates the schematic of the 2006 Guidelines; and provides the rationale used by the Panel for these changes. This report is intended to help prehospital-care providers in their daily duties recognize individual injured patients who are most likely to benefit from specialized trauma center resources and is not intended as a mass casualty or disaster triage tool. The Panel anticipates a review of these Guidelines approximately every 5 years.