A state-of-the-art summary from leading laboratories around the world of our current knowledge of the molecular biology, the physiology, and the pharmacology of the P2 receptors. The authoritative contributions cover the major aspects of these receptors, describing the relationships between physiological and pharmacological effects of ATP and other nucleotides and the various cloned P2 receptors, as well as providing an historical perspective and discussing current issues of nomenclature. They also illuminate how P2 receptor structures contribute to their function, including the physical differences underlying the pharmacological and functional variations among P2 receptor subtypes.