In addition to designing catalytic materials ever more active and selective, the emergence of new classes of greener catalysts remains very challenging. The apatite family system with hydroxyapatite (HA) structure appears as a good candidate for catalysis due to its eco-compatibility properties, its sorption ability toward organic molecules, and its tunable composition resulting into modulation of its surface properties. Depending on their mode of preparation, these inexpensive and environment-friendly apatitic calcium phosphates exhibit properties of relevance to catalysis, such as large surface area and various morphologies. However, most studies focused so far on the catalytic performance of these compounds, while the study of structure–reactivity relationships required for rationalized optimization remains rather limited. This chapter aims at providing tools to help understand the catalytic behavior of apatite compounds, giving details about their structure, surface properties, and reactivity; this will include both stoichiometric and nonstoichiometric compounds, sometimes biomimetic and potentially substituted. A special attention is dedicated to recent advances in the characterization of their structural properties (bulk and surface/interphase) that have a strong impact on their reactivity, through both experimental and computational approaches to study the mechanisms occurring in the structure or at the crystals surface, as well as thermodynamic and dynamical properties. Remaining characterization challenges for apatite-based catalysts will also be discussed.