Myalgic Encephalomyelitis / Chronic Fatigue Syndrome: Clinical Working Case Definition, Diagnostic and Treatment Protocols presents an important medical milestone--a clinical definition (clinical diagnostic criteria) for myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). The clinical case definition was developed by an expert medical consensus panel of treating physicians, teaching faculty and world leaders in the research of ME/CFS. An expert subcommittee of Health Canada established the Terms of Reference for the consensus panel. The definition more adequately reflects the complexity of symptoms of a given patient's pathogenesis and should establish ME/CFS as a distinct medical entity and help distinguish it from overlapping medical conditions in the absence of a definitive laboratory test. This special issue of the Journal of Chronic Fatigue Syndrome also includes a discussion of prominent symptoms, clinical practice diagnostic and treatment guidelines based on the best available research evidence, and an overview of available research on ME/CFS.