The mineralization and demineralization processes of the calcified tissues of higher vertebrates are considerably affected by the incorporation of alkalimetal (especially Na⁺) and CO₃^2- in their calciumhydroxyapatite (HAp) phase. This paper compiles our work on Na⁺, K⁺ and CO₃^2- incorporation in synthetic HAp. It was shown that, although CO₃^2- can substitute OH^- ions in apatites prepared in aqueous solution, solid state reactions at high temperature are required to obtain considerable amounts of this type of CO₃^2-incorporation. For the incorporation of CO₃^2- on PO₄^3- lattice sites, the predominant mechanisms compare quite well for all apatites. Whereas mechanism (Ca²⁺ + PO₄^3- + OH^- ↔ V^Ca + CO₃^2-  + V^OH) mainly accounts for the individual CO₃^2- for PO₄^3- incorporation, mechanism (Ca²⁺ + PO₄^3- ↔ M⁺ + CO₃^2-) is the main mechanism for the alkali metal (M⁺) incorporation in HAp, which thus seems to be coupled with the CO₃^2- incorporation. (V^x is a vacancy on a regular apatite lattice site occupied by X.) However, Na⁺ can also be incorporated in the apatite lattice individually according to mechanism (Ca²⁺+ OH^- ↔ M⁺ + V^OH). The driving force and hence the contributions of these mechanisms are determined by the preparation conditions, such as the crystallization mechanism, the ionic concentrations and the type of alkalimetal in the reaction medium, e.g. Na⁺ is incorporated to a much larger extent than the voluminous K⁺ ion. Moreover, variation of the precipitation conditions of the apatites revealed that, although there is no intrinsic coupling between the fundamental substitution mechanisms, an indirect correlation can occur. The incorporation of M⁺ and CO₃^2- in HAp affects the physical properties of the solid solution, e.g. their lattice parameters and their infrared absorption characteristics.