This two-volume book provides the first comprehensive survey of opioid research, a field which has accumulated a tremendous amount of literature since the identification of opioid receptors and their endogenous ligands. In more than 60 chapters experts present state-of-the-art reviews of this fascinating field, the topics ranging from molecular biology to clinical applications. Part I covers the multiplicity of opioid receptors, the chemistry of opiates and opioid peptides as well as the neurophysiology of opioids. Part II reviews a broad spectrum of physiological and behavioral functions and pharmacological actions of opioids, together with their neuroendocrinology, opioid tolerance and dependence, concluding with pathophysiological aspects and clinical use.