In the first place may I say how grateful I and others are to those who have contributed chapters for this book; all of them are well known for their research on the subject on which they have written and each has indicated the background to his own specialist field by providing an extensive bibliography giving this book a total reference list of over 2,500. Although there have been enormous advances in immunology over recent years, much of the new knowledge in relation to infectious diseases was scattered over the world's literature and is now brought together in a single volume. Furthermore, while a number of previously unknown infectious diseases have recently been discovered (e.g. Marburg and Lassa virus infections and Legionnaires' disease) to which many new techniques have been applied, there seemed to be no clear statement of the rationale for their use, or for their further exploitation in some of the more common infectious diseases which are discussed in this book.