Pain has many valuable functions. It can be a warning or force us to rest our bodies. Yet most ongoing chronic pain, such as unrelenting backache or headache, has no discernable cause and diminishes countless lives. Over the years a scientific revolution has taken place in chronic pain research and therapy.A major catalyst for this was the introduction of the ‘gate theory’ by Professor Ronald Melzack and Professor Patrick D.Wall, which argued that pain is a unified stream of experience generated by the brain, incorporating a whole host of psychological functions.Their now-classic book, with a new introduction taking in all the latest medical developments, examines every facet of pain: the psychological and clinical aspects, the physiological evidence, the major theories of pain and the developments in its control. The challenge in the twenty-first century is to look at how memories, personal and social expectations, genetics, gender, aging and stress patterns all play a role in pain, and how understanding this could lead to the relief of the suffering endured by millions.