Recent years have witnessed an explosion of knowledge lea- ding to a molecular understanding of the mechanisms of ac- tion of calcium on excitation and contraction coupling and its role in the regulation of contractility. This book highlights the most recent progress as well as providing a historial perspective of the field. It presents a concise and comprehensive overview of our current knowledge regar- ding calcium channels and regulatory proteins as well as in- tracellular calcium handling and the mechanisms underlying the activation of contractile proteins. It also describes how these basic mechanisms have been adapted in various types of muscle, especially in cardiac and smooth muscle.