Dental caries is an infectious and transmissible disease. The mutans streptococci (MS) are infectious agents most strongly associated with dental caries. Earlier studies demonstrated that infants acquire MS from their mothers and only after the eruption of primary teeth. More recent studies indicate that MS can colonize the mouths of predentate infants and that horizontal as well as vertical transmission does occur. The purpose of this paper was to demonstrate that these findings will likely facilitate the development of strategies to prevent or delay infant infection by these microbes, thereby reducing the prevalence of dental caries.