Immunology is a fascinating discipline at the heart of many new medical treatments, including vaccines, organ transplants, and cancer therapies. During the fall semester, I am the course organizer and primary lecturer of Immunology 528 (PBS/MMI 528), a three-credit class with upper-level undergraduates and graduate students. This course introduces the principles of immunology, starting with the basics of adaptive and innate immune cells and associated immune molecules. It builds upon this foundation to cover major histocompatibility complex (MHC) immunogenetics and antigen presentation, the fundamentals of antigen receptor diversity, and the mechanisms of B and T cell activation. Lastly, we apply these principles to examine how the immune system attacks infectious diseases and eliminates tumors, and the pathogenic consequences of immune dysfunctions.