Since Smythe and Moldofsky proposed the first modern definition of fibromyalgia (FM), a number of different classification and diagnostic criteria have emerged. Among these criteria, the 1990 American College of Rheumatology (ACR) classification criteria have been the most widely accepted in both research and clinical settings. The 1990 ACR criteria were originally established as inclusion criteria for research purposes and were not intended for clinical diagnosis, but have become the de facto diagnostic criteria in clinical settings. However, an improved clinical case definition for FM, using diagnostic criteria that can be used by both primary care physicians and specialists has been desired for a long time. For this, Wolfe and colleagues developed several sets of diagnostic criteria and their last one received the endorsement of ACR, which is now known as the 2010 ACR diagnostic criteria. Unfortunately, the new criteria have been criticized as being inconsistent, non-specific, and lacking the ability to recognize FM concurrent with other diseases. Further studies are needed to assess the acceptance, reliability, and validity of the new criteria in epidemiologic and clinical studies.