The sixth edition of Basic Immunology has been revised to include recent important advances in our knowledge of the immune system. The original goals of this book，from the earliest edition， were to present current con-cepts in immunology cogently and also in sufficient detail that they would be understood by students of the discipline， as well as to emphasize clinical aspects，including disease pathogenesis and the development of novel therapies based on the basic science ofimmunol-ogy. These are the goals that we continue to strive for.With improving understanding of the normal immune response， we believe it is possible to present the funda-mental knowledge in a concise way. In addition， there has been exciting progress in applying basic principles to understanding and treating human diseases， a topic that is of paramount interest for students of medicine and allied health sciences. Foremost among these recent
　　advances is the development of cancer immunotherapy，which dramatically illustrates how foundational saence can be translated into clinical practice.
　　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.
　　We hope that students will find this new edition of Basic Im m u n ology clear， cogent， manageable， and enj oy-able to read. We hope the book will convey our sense of excitement about how the field has evolved and how it continues to grow in relevance to human health and disease. Finally， although we were spurred to tackle this project because of our associations with medical school courses， we hope the book will be valued by students of allied health and biology as well. We will have succeeded if the book can answer many of the questions these stu-dents have about the immune system and， at the same time， encourage them to delve even more deeply into immunology.
　　Several individuals played key roles in the writing of this book. Our editor， James Merritt， has been an enthu-siastic source of encouragement and advice. Our tal-ented illustrator， David Baker， continues to effectively convert our ideas into pictures that are informative and aesthetically pleasing. Our development editor， Rebecca Gruliow， has kept the project organized and on track despite pressures of time and logistics. Clay Broeker has moved the book through the production process in an effiaent and professional manner. To all of them we owe our many thanks. Finally， we owe an enormous debt of gratitude to our families， whose support and encouragement have been unwavering.