Medical immunology is the study of how the human body responds to disease. As such, it is a foundational science for pathology and clinical practice. It is also arguably the most poorly taught of subjects in medical school, and it is not a subject that can be conquered through memorization. This book reflects the experience of 30 years teaching in the field, converting the molecular complexities of the immune system into a memorable, logical engineering design. Initially, the development of immune cells is followed from their origin in the bone marrow, through their training in primary lymphoid organs, and their recirculation and homing into the lymph nodes and spleen. From there, the sequence of innate inflammation is followed through the potential development of cell-mediated and humoral adaptive immune responses. Once the design of the system is explained, the clinical applications of the immune response in vaccination, diagnosis, and management of immunodeficiency and hypersensitivity diseases, HIV infection, transplantation, and neoplasia. The delivery of this material in a logical and memorable design which emphasizes understanding will serve as the foundation for a great score on board exams, and the basis for a lifetime in learning the new frontiers in this rapidly evolving discipline.