Fibromyalgia syndrome (FMS) is characterized by chronic widespread pain and various accompanying symptoms including fatigue, sleep disturbances, and cognitive dysfunction. While the etiology of fibromyalgia is unclear, accumulating data suggest that disordered central pain processing likely plays a role in the pathogenesis of symptoms. Although the 1990 American College of Rheumatology (ACR) classification criteria for FMS were originally developed for research purposes and were not intended for clinical diagnosis, the criteria have become the de facto diagnostic criteria in clinical settings. Recently, an improved clinical case definition for FMS was proposed by ACR in 2010 to overcome several limitations of 1990 ACR criteria. Further studies are needed to assess the acceptance, reliability, and validity of the new criteria in epidemiologic and clinical studies. Many randomized controlled trials and meta-analyses confirm the therapeutic efficacy of pregabalin, duloxetine, and milnacipran, in the treatment of FMS. In view of the currently available evidence, a combination of pregabalin, duloxetine, or milnacipran as pharmacological interventions and aerobic exercise or CBT as non-pharmacological interventions seems most promising. (Korean J Med 2013;84:650-658)