The seriousness and societal costs of dental caries in preschool children are enormous. National data shows that caries is highly prevalent in poor and near poor US preschool children, yet this disease is infrequently treated. The etiology includes elevated colonization levels of mutans streptococci, high frequency sugar consumption, and developmental defects on primary teeth. A necessary first step in preventing dental caries in preschool children is evaluating the child's caries risk factors that include socioeconomic status, previous carious experience, presence of white spot lesions, presence of visible plaque, perceived risk by dental professionals, and microbiologic testing for the presence or quantity of mutans streptococci. Based on this knowledge, different preventive strategies, as well as different intensities of preventive therapies, can be employed. Caries preventive strategies in preschool children include diet modifications to reduce high frequency sugar consumption, supervised tooth brushing with fluoridated dentifrice, systemic fluoride supplements to children living in a nonfluoridated area that are at risk for caries, professional topical fluoride with fluoride varnish, and sealants for primary molars.