Finn Brudevold was a distinguished leader in dental research, recipient of many honors, and a Past President of IADR. This article traces his scientific career and focuses on his discovery and development of acidulated phosphate fluoride (APF) for practical use in caries prevention. Brudevold noticed that the low pH of stannous fluoride was very effective in getting fluoride into enamel in vitro. He hypothesized that an acidulated preparation that included phosphate to minimize enamel dissolution by a common ion effect would permit faster exchange of hydroxyls with fluoride. The clinical efficacy of APF is compared with other methods of professionally applied topical fluoride agents.