Galvanized by the seminal publication of the Institute of Medicine’s report To Err Is Human: Building a Safer Health System in 1999, the patient-safety movement has resulted in substantial improvements in the safety and quality of the care delivered by hospitals. A number of techniques and process-improvement tools from inside and outside the industry have been brought to bear: lean engineering to simplify and standardize care, Crew Resource Management to improve teamwork, checklists to help teams focus and improve reliability, and so on. Human factors science, which studies the relationship between human beings and systems in order to improve efficiency, safety, and effectiveness, is now being applied broadly in health care in everything from information management to the design of operating rooms.