Gaining an understanding of the mechanisms by which cells process and respond to extracellular cues has become a major goal in many areas of bi- ogy and has attracted the attentions of almost every traditional discipline within the biological sciences. At the heart of these divergent endeavors are common methods that can aid biochemists, physiologists, and pharmacologists in ta- ling the specific questions addressed by their research. In Receptor Signal Transduction Prools, a diverse array of meth- ologies employed to interrogate ligand—receptor and receptor-effector int- actions are described by authors who have devised and successfully applied them. The authors blend excellent descriptions and applications of fairly well established methodologies with new technologies at the cutting-edge of signal transduction research and as such I hope the present volume will complement and extend a previous excellent volume in this series edited by David Kendall and Stephen Hill (Methods Molecular Biology, vol. 41, Signal Transd- tion Prools).