This book is about the recent advances in the structural and functional characterization of receptors that influence intracellular signalling events through interaction with intracellular GTP-binding proteins (G proteins). Molecular cloning of members of the G protein-coupled receptor superfamily has complemented pharmacological investigations in providing a realization of the structural and functional diversity of these receptors. An increased understanding of the involvement of particular receptor subtypes in normal and pathophysiological processes represents exciting possibilities for the development of highly specific and effective therapeutic agents.