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����More specifically��we have focused on the following objectives.First��we have presented the most important principles governing the function of the immune sys-tem by synthesizing key concepts from the vast amount of experimental data that have emerged in the field of immunology.Our judgment of what is most important is based largely on what is most clearly established by scientific investigation and is essential for understand-ing the major functions of the immune system.We have also prioritized content that is relevant to human health and disease.We have realized that in any con- cise discussion of complex phenomena��it is inevitable that exceptions and caveats cannot be considered in detail��so these have largely been omitted.Second��we have focused on immune responses against infectious microbes��and most of our discussions of the immune system are in this context.Third��we have made liberal use of illustrations to highlight important principles��but we have reduced factual details that may be found in more comprehensive textbooks.Fourth��we have also discussed immunologic diseases from the perspec-tive of principles��emphasizing their relation to normal immune responses and avoiding details of clinical syn-dromes and treatments.We have included selected clin-ical cases in an appendix to illustrate how the principles ofimmunology may be applied to common human dis-eases.Finally��in order to make each chapter readable on its own��we have repeated key ideas in different places in the book.We feel such repetition will help students to grasp the most important concepts.