Chronic pain is pain without a clear somatic substrate. As a result, patients with chronic pain often do not receive a clear diagnosis following a medical examination. In many patients, having pain without a proper explanation or diagnosis induces stress and the urge to search elsewhere for explanations and treatments. There is growing evidence that many chronic-pain syndromes, such as chronic low-back pain, whiplash and fibromyalgia, share the same pathogenesis: sensitisation of pain-modulating systems in the central nervous system at both spinal and supraspinal level. This central sensitisation is facilitated by numerous factors that contribute to the maintenance of pain in a way that differs from individual to individual. How sensitisation may develop and persist as a result of medical, psychological and social factors calls for research from the perspective of a bio-psycho-social model. If sensitisation is used to explain chronic pain to a patient and the patient understands the relation beween pain and the factors that play a role in the maintenance of the pain, this can lead to acceptation of a treatment learning to cope with these factors.