Chronic widespread musculoskeletal pain (CWP) is the cardinal symptom of fibromyalgia. The definition emphasizes axial pain, as well as the presence of pain in the upper and lower quadrants, and the right and left sides of the body. The chronic pain syndromes (CPS) are a poorly defined constellation of syndromes with ongoing pain that show overlap in presenting symptomatology such as fatigue, sleep disturbance, anxiety, depression, headache, and functional bowel disturbance. Chronic pain syndromes (CPS) are highly prevalent in the general population, and increasingly the evidence points to a common etiological pathway. CWP has a reported prevalence in the general population of approximately 15%. CWP not only causes profound individual suffering and disability in activities of daily living but is also associated with high health care utilization and increased health care costs. CPS are a serious challenge to health care providers because of their unclear and complex multifactorial pathophysiology, psychological element, and poor response to therapy. Knowledge about the causes of chronic pain remains very limited but current research suggests that the pathology and its somatic expression are influenced by genetic susceptibility - epigenetic factors are also implicated.