In this section we categorize the major applications of information theory to physical systems and provide the major references defining the interface. General works relating information to physics are noted, and then the major contributions stemming from utilization of the maximum entropy principle are surveyed. We next provide a sampling of the literature describing information-theoretic methods in various subfields of physics, the aim being to provide examples of how specific disciplines have adapted this tool. Finally, a few fields have been singled out for more detailed discussion because they are areas in which information-theoretic ideas are playing a principal role in very active current research.