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 of CaPO4 as biocomposites and hybrid biomaterials, self-setting formulations, as well as the workings of their dissolution mechanism. Topics discussed include the major constituents of biocomposites and hybrid biomaterials for bone grafting, preparation, properties and the available knowledge on interactions among the phases for various types of CaPO4-based biocomposites. Additionally, the major types, preparation, properties and the available knowledge on the reinforced formulations for various types of self-setting CaPO4-based compositions, followed by the detailed description of their biomedical applications and in vivo behaviour are discussed. The comprehensive description of currently available dissolution mechanisms of calcium apatites in acids, followed by the successful attempt to create the general dissolution mechanism is given in the last section of this book.