This second edition of Receptor Signal Transduction Protocols not only has a new editor, but also a greater focus on G-protein-coupled receptors, their properties per se, and their coupling to immediate downstream binding partners—principally, although not exclusively, the heterotrimeric G-proteins. The new edition combines updates of key chapters from the first edition, as well as a large number of new contributions covering key methodologies that have emerged, or been extended to receptor/G-protein research, in the past 5–6 years. In common with many fields, the range of methods used to assess the first steps in signal transduction are continually expanding and methods that might have been considered too specialized five years ago are now sufficiently routine to be included here. Unlike many research areas, where off-the-shelf kits have made research basically foolproof, signal transduction research still requires considerable expertise, and the methods included here are provided by internationally recognized experts in their fields who have many years of experience using the methods they describe. This not only allows each chapter to impart a clear description of the method, but also to furnish invaluable troubleshooting advice for when things do not go entirely according to plan. Once again we would like to thank the Series Editor, John Walker, for the invitation to compile this second edition, and to express our gratitude to all of the authors who have enthusiastically agreed to provide the uniformly excellent contributions.