The caries preventive effect of fluorides has been known since the 1930s, when the differences in caries prevalence between communities were attributed to naturally occurring fluoride levels in the drinking water. Due to its safety, efficacy and cost-effectiveness in preventing caries the use of fluorides in various forms thus remains cornerstone of most caries prevention programs. The humans are exposed to fluoride on the human organism knowledge of fluoride metabolism is necessary. It is seen that anti caries effect is most pronounced when a low level fluoride is constantly maintained in the oral cavity, though the respective roles of pre-eruptive and post-eruptive fluoride continues to be debated. This chapter describes the mechanism of action of fluorides, its metabolism and various methods of administration both topical and systemic.