Dental caries has declined in the 40 years since fluoridated toothpastes were introduced. Much has been learned about why fluoride is so effective and how this knowledge can be used to optimise programmes for caries prevention. Fluoride works through enhancing the remineralisation of early stages of caries and by inhibiting demineralisation, which would lead to dental caries. Remineralisation involves the deposition of calcium phosphates from saliva to rebuild partly dissolved enamel crystallites. When fluoride is incorporated the dissolution of these reinforced crystallites will be reduced during a subsequent sugar-induced and bacteria-mediated acid attack. Fluoride works primarily when it is present in the oral cavity. Based on our understanding of the fluoride mode of action the following advice can be given from clinicians to their patients: The fluoride concentration in oral products is related to efficacy but the concentration does not necessarily need to be high to be efficacious. Fluoride availability throughout the day is important; this can be achieved when fluoride products are used as part of the daily hygiene routine (F-brushing or rinsing). Alternatively, when fluoride is provided in the drinking water or through professionally applied F-varnishes or gels, the patient will benefit without requiring daily compliance to its use. The latter methods are particularly effective as additional treatments in high caries individuals.