Since first shown to be effective by Bibby in 1942, professionally applied topical fluorides have been used successfully as a caries-preventive intervention. In the United States, the acidulated phosphate fluoride (APF) gels have been the most widely used agent for over two decades. While effective, APF has several practical disadvantages, including unpleasant taste and the risk of fluoride overingestion. The use of APF on infants and very young children is not practical or safe. Recently, fluoride varnish has become available in the United States. It has been used widely in Europe and Scandinavia for 25 years. Its effectiveness and safety are documented in over 50 clinical trials. Fluoride varnish is easy to apply, is well accepted by children, and eliminates the risk of overingestion of fluoride. Fluoride varnish is approved by the FDA as a "device" and must be used "off label" for the prevention of caries. Because of the large body of published data documenting its effectiveness and safety, there is no legal risk in using fluoride varnish off label. In fact, the American Dental Association has granted its seal of approval to Duraphat, one of the varnish products. Varnish offers considerable advantages in the dental public health setting. Of particular note, it is practical and safe to apply to the teeth of infants and very young children.