Immune cells are part of the most dynamic organ system in the body, which fights primarily against infections and maintains cellular integrity and homeostasis. Memory is a unique feature of the immune system, which enables immune cells to remember previous antigen exposure and to respond effectively upon rechallenge throughout lifetime. Immunological memory is the key feature which has helped to develop vaccines against a variety of diseases. However, the development, differentiation, and responsiveness of the many innate and adaptive immune cells are largely encoded in their genetic and epigenetic makeup. Though the genetic codes have been important in shaping person-specific immune responses, the (micro)environmental stimuli contribute most effectively to the shaping of molecular and cellular responses. Thus, a holistic understanding of the interface of epigenetics and the immune system is absolutely necessary. In this chapter, we introduce readers to the key concepts in immunology and epigenetics. Furthermore, we will conclude with a glimpse of the interdisciplinary future of epigenetics of the immune system.