Health care quality means that patients receive appropriate care for medical problems in order to achieve the best possible outcomes. Quality of care is a cooperative effort that involves patients, doctors, nurses, and other health care professionals, as well as institutions (such as hospitals, nursing homes, mental health centers, and home health care agencies). Part of providing quality health care involves following standards, guidelines, and evidence-based practices. Evidence-based medicine involves using results from research studies such as clinical trials (scientific tests of treatments) and findings from other investigations to guide medical decisions. When results from such research indicate that a particular way of treating a disease is best, guidelines are developed to help clinicians and patients make good decisions about medical care. The October 22/29, 2008, issue of JAMA is a theme issue on the health of the nation and includes articles about the US health care system.