This course enables student dentists to understand how microorganisms live and infect humans and how humans respond to these infections to preserve health. Part I of the course presents basic microbial structure, function, and genetics; and principles of chemotherapy and drug resistance. Part II covers mammalian host defenses and the molecular basis of immunity. Part III presents the biologic and clinical basis of infectious diseases of all major organ systems including the mouth. The course focuses on the mechanism of pathogenesis and the common features of all forms of parasitism beginning with the encounter of the host with the microbe and ending with the outcome - the host wins, the microbe wins, or they coexist. Dental examples are used where possible so that student dentists will be able to more readily apply concepts to the diagnosis, therapy, and prevention of infectious diseases of the mouth and contiguous tissues that they encounter later in the curriculum and in their practice of dentistry. Lecture: 103 hours.