Early childhood caries (ECC) is a virulent form of dental caries that can destroy the primary dentition of toddlers and preschool children. It occurs worldwide, afflicting predominantly disadvantaged children. High-risk North American populations include Hispanic and Native American children, as well as children enrolled in Head Start, a federally funded program for preschool children living in poverty. The prevalence of EEC among these children ranges from 11% to 72%. ECC is an infectious disease, and Streptococcus mutans is the most likely causative agent; diet also plays a critical role in the acquisition and clinical expression of this infection. Early acquisition of S. mutans is a key event in the natural history of the disease. Acquisition may occur via vertical or horizontal transmission. Primary oral colonization by S. mutans coupled with caries-promoting feeding behaviours results in accumulation of these organisms to levels exceeding 30% of the total cultivable plaque flora which in turn leads to rapid demineralization of tooth structure. Treatment of ECC is costly because the cooperative capacity of babies and preschool children usually necessitates the use of general anesthesia. Treatment usually consists of restoration or surgical removal of carious teeth along with recommendations regarding feeding habits. However, this approach has resulted in unacceptable clinical outcomes, and relapse rates of approximately 40% have been reported within the first year after dental surgery. Primary prevention of ECC has largely been restricted to counselling parents about caries-promoting feeding behaviours. This approach has also had minimal success. Newer strategies addressing the infectious component through use of topical antimicrobial therapy appear promising.