Like all of the previous authors of this book, we are dedicated to the concept that immunology is best taught and learned in an experimentally based manner, and we have retained that emphasis with this edition. It is our goal that students should complete an immunology course not only witha firm grasp of content, but also with a clear sense of how key discoveries were made, what interesting questions remain, and how they might best be answered. We believe that this approach ensures that students master fundamental immunological concepts, internalize a vision of immunology as an active and ongoing process, and develop the ability to contribute to new knowledge, themselves. Guided by this vision, this new edition has been extensively updated to reflect the recent advances in all aspects of our discipline.