The present overview is intended to point the readers' attention to the important subject of calcium orthophosphates. This type of materials is of the special significance for the human beings because they represent the inorganic part of major normal (bones, teeth and antlers) and pathological (i.e. those appearing due to various diseases) calcified tissues of mammals. For example, atherosclerosis results in blood vessel blockage caused by a solid composite of cholesterol with calcium orthophosphates. Dental caries and osteoporosis mean a partial decalcification of teeth and bones respectively that results in replacement of a less soluble and harder biological apatite by more soluble and softer calcium hydrogenphosphates. Therefore, the processes of both normal and pathological calcifications are just an in vivo crystallization of calcium orthophosphates. Similarly, dental caries and osteoporosis might be considered as in vivo dissolution of calcium orthophosphates. Conversely, due to a great chemical similarity with the biological calcified tissues, many calcium orthophosphates possess remarkable biocompatibility and bioactivity. Materials scientists extensively use this property to construct artificial bone grafts that are either entirely made of or only surface-coated by the biologically relevant calcium orthophosphates. For example, self-setting hydraulic cements made of calcium orthophosphates are helpful in bone repair, while titanium substitutes covered by a surface layer of calcium orthophosphates are used for hip joint endoprostheses and tooth substitutes. Porous scaffolds made of calcium orthophosphates are very promising tools for tissue engineering applications. In addition, calcium orthophosphates of a technical grade are very popular mineral fertilizers. There is a great significance of calcium orthophosphates for the humankind and, in this paper, an overview on the current knowledge on this subject is provided. To assist and guide the readers, a great number of references to the related publications detalizing various specific aspects of the matter has been collected.