The aim of this book is to introduce the medical student, recent medical graduates involved in postgraduate training and physicians in practice to the role of the platelet in physiology and disease. It is not intended to be an encyclopaedic review of all the literature over the past few decades, but largely represents a personal account, and although resultant prejudices occur, an attempt has been made to emphasize to the reader areas of doubt, and point the way to other sources which may explore these questions more fully in selected references at the end of each chapter. I acknowledge the help of my secretaries, Ms Carolyn Harvey and Mrs Marjorie Brown without whom the book would never have been started, let alone completed. Some illustrations and figures were made by Mr W. Shepherd of Monash University and Ms A. Leaman of the Alfred Hospital. I am indebted to Mrs E. Hagon who read and corrected a number of the chapters, and for the constant help through discussion and debate with my two close collaborators in research, Dr Margaret Howard and Dr Sharron pfueller. Dr Siew Choong, Mrs Maureen Broadway and Ms Ilona Lakatos documented the methods used in our laboratory to study platelets as outlined in the Appendix.