This volume provides a compilation of the main principles of signal transduction mechanisms. The reader will become familiar with the most recent developments on: - the structure and function of heterotrimeric G-proteins and their receptors; - the small GTPases Ras, Rho, Rab and Arf; - EGF receptor, Ca2+ and protein kinase C; - phosphoinositide kinases (PI-3 kinases); - phospholipases C and D; - ceramides and possible modulators of apoptosis; - transcription factors and gene activation; - multidrug resistance transporters.