Studies of synthetic and biological calcium phosphates (Ca-Ps) improve our understanding of dental calculus, dental caries and the biological fate of Ca-P biomaterials used as bone grafts. This monograph provides an overview of the preparation and physicochemical characterization of Ca-Ps, their transformation or interconversions in vitro and their biological occurrences. The effect of elements like fluoride, carbonate, magnesium, strontium and zinc on the formation and stability of apatites and related Ca-Ps are presented in detail, and new information on factors promoting and inhibiting the formation of Ca-Ps and calcium fluoride is given.