Functional immunology has become the most important clinical issue of our time. To a great extent this is due to the impact of SARS-CoV-2 variants on global health, but it is also a consequence of the recognition that virtually every major chronic health issue is connected to imbalances within the immune system. We are witnessing a conceptual shift in thinking—from immunity as a generic and passive phenomenon to immunity as highly personalized and uniquely dynamic in response to the interplay among genetics, lifestyle, diet, and environmental exposures.