The immunology of infectious disease involves studies of how the immune system responds to infectious agents and how infectious agents interact with, modify or evade the immune system. In recent years there have been major advances in our understanding of the immune response to infection. One of the major advances has been the recognition of the link between the innate and adaptive immune systems in responding to infection. Mammalian cells involved in innate immune defenses have pattern recognition receptors that allow the host to detect conserved features of infectious agents such as viral nucleic acid or bacterial cell wall components. These pattern recognition receptors are crucial for activating the innate immune system and rendering cells called antigen-presenting cells capable of activating T cells of the adaptive immune system. There is currently much interest in understanding how the immune system recognizes different features of infectious agents and how it translates these signals to allow the appropriate immune response to effectively control the pathogen. Another major advance has been the development of approaches and reagents to carefully follow antigen-specific T lymphocyte responses to infectious agents using intracellular cytokine staining and MHC tetramers. These tools are providing important insights into how the immune response to infectious agents develops over time. Immunological memory, the ability to rapidly recognize and respond to pathogens based on prior exposure, is the basis upon which vaccines to infectious agents are developed. Thus an important area of investigation is to understand the features of the infectious agents and the immune system that lead to induction and maintenance of immunological memory. In addition to the direct effects of infectious agents, it is becoming increasingly apparent that the host response to infection combined with genetic susceptibilities can contribute to conditions such as Crohn’s disease or reactive arthritis. Therefore understanding the detailed interactions between pathogens and the immune system and determining the correlates of protection versus pathology are critical for understanding and controlling both infectious diseases and a number of infection-related autoimmune conditions.