The tooth surfaces are unique in that they are the only body part not subject to metabolic turnover. Once formed, the teeth are, under the correct conditions, essentially indestructible, as witnessed by their importance in fossil records and forensic medicine. Yet in the living individual, the integrity of the teeth is assaulted by a microbial challenge so great that dental infections rank as the most universal affliction of humankind. The discomfort caused by these infections and their enormous cost (dental infections rank third in medical costs, behind heart disease and cancer, in the United States) gives dental diseases prominence despite their non-life-threatening nature. This book reviews the bacterial aspects of dental caries and suggests that, in the future, treatment will be directed toward eliminating or suppressing certain bacterial species that appear to be overt pathogens in the dental plaque.