Originally based on a graduate course taught by the author, this well-known textbook has again been extensively updated to incorporate key new findings in biological signaling, e. g. in the structural biology of GPCRs, scaffolding and regulation of signaling networks, and RNA silencing. At least 50 % of the text has been re-written, and 70 new full color figures have been added. With its clear and concise style, full-color figures, and newly added study questions for each chapter, this textbook excels as a companion for a course on biological signaling as well as an introductory reference to the field for students and researchers.