As the inorganic constituents of skeletons, dentine and the enamel of teeth in all vertebrates, as well as antlers of male deer, calcium orthophosphates (CaPO4) appear to be the key materials to sustain all life on Earth. Therefore, biologically relevant CaPO4 possess all the necessary features of the biomaterials, such as biocompatibility, bioactivity, bioresorbability, osteoconductivity, osteoinductivity, and appear to be non-toxic, non-inflammatory and non-immunogenic. In this book, the author presents current state-of-the-art applications on three popular types of CaPO4: nano-scaled (nano-dimensional), multiphasic (polyphasic) and amorphous CaPO4. Topics discussed include the preparation, structure, composition, properties and biomedical applications of these types of CaPO4 combined with the specific information for each type. Namely, occurrence in the calcified tissue of mammals is discussed for both nano-scaled and amorphous types of CaPO4; both known and potential formulations, as well as their stability are discussed for multiphasic CaPO4, while both the morphology and the available knowledge on amorphous-to-crystalline transformations are discussed for amorphous CaPO4.