Dental caries is a multifactorial, infectious disease affecting a significant percentage of the population. It is more accurate to consider caries as caused, not by an infectious agent, but by a shift in oral microflora to caries-causing types in response to acidity resulting from metabolism of sugars. The development of caries is dependent on the interaction of four primary factors. These are a host (tooth surface), a substrate (food), the presence of oral bacteria, and time. Caries will not develop if any of these four primary factors are not present. Understanding the etiology and pathways of progression of dental caries will enable the profession to strive toward early intervention and, hopefully, prevention.