The mechanism of information transfer between cells is the subject of this text. In the past, aspects of this field were the domain of different disciplines, including endocrinology, neurochemistry, and pharmacology. However, in recent years, signal transduction has emerged as an independent discipline. This book covers the major topics in signal transduction: receptors which recognize the signal molecules at the cell surface; G-proteins which induce the signals; and adenylate cyclases, granylate cyclases, and prospholipases which generate the second messenger. The discussion focuses on ion channels, prosphodiesterases and protein kinases, which participate in the ultimate cellular response to signals, the health consequences of defects in signal transduction proteins, and the central role signal transduction plays in drug abuse. This volume is designed to be a reference source for investigators in the field, and is aimed at students interested in an overall understanding of the concepts involved in cell signalling. The topics are covered with the goal of preparing the reader for an in-depth examination.