This book offers a comparative and interdisciplinary approach to excitation-contraction-coupling in smooth and striated mus cles, including the myocardium. It is an account of the path ways and mechanisms by which cellular calcium is handled and activates the contractile proteins. It also describes how these mechanisms are adapted in various kinds of muscle to meet specific functional requirements, such as speed or economy. This monograph then presents facts, ideas and theories and the evidence on which they are based, and ifit stimulates others and furthers research, it will have served its purpose. All of the chapters are self-contained and may be read in any order, but readers unfamiliar with muscle are recommended to start with the introductory chapter on excitation and contraction. During all the years of writing this book, I received enormous help from Isolde Berger who corrected, edited and transformed my innumerable notes and drafts into a readable manuscript; she also compiled the list of references and the Subject Index. I owe a great debt of gratitude to her and also to Claudia Zeugner, who prepared the figures with expertise and care. Then I would like to thank the Deutsche F orschungs gemeinschaft and the Fritz-Thyssen-Stiftung for supporting the work of my Department which has been reported in this monograph. A great many people contributed with helpful discussions.