This textbook is based on the curricula for dental students in the Nordic countries, and the authors teach the subject at three universities in Denmark, Norway and Sweden. Although primarily for undergraduates, the book may also appeal to Ph.D. students and general practitioners. In addition, dental assistants and trainees may find it a useful source of reference. The contents are based on general microbiology and immunology. Oral microbiology is given particular attention, with examples relevant to oral infectious diseases. Each chapter opens with a relatively short pre-reading section, followed by a fact box containing most of the relevant basic definitions concerning the particular chapter. The body of the text is supplemented with more fact boxes and the essentials of each section are summarised in main points. It is the authors' intention that each chapter should be read as a self contained unit. This has resulted in deliberate repetition and cross-reference within and between chapters.