Nanocrystalline apatites constitute the main inorganic part of human hard tissues (bone and teeth), and a growing focus is devoted to prepare synthetic analogs, so-called "biomimetic", able to precisely mimic the morphological and physical-chemical features of biological apatites. In fact, it is reasonable to hypothesize that by virtue of their high similarity with the biogenic calcium phosphates, synthetic nano-sized and ionic substituted apatite nanocrystals can display better biological performances than coarser and ceramic hydroxyapatite. For this reason, the study of their crystallization mechanisms and the possibility to tailor the structural and physical-chemical properties of these materials open several possibilities to prepare optimal devices in medical sciences and also to better investigate the biomineralization processes of living organisms. This book is divided in three main parts and is principally devoted to highlight the recent progresses on the preparation and characterization of multifunctional nanocrystalline apatites with tailored properties to be used as healthcare materials (i.e. nanoparticles for drug or gene delivery and materials for bone substitution and regeneration). The first part is intended to be a comprehensive review of the importance and the occurrence of calcium phosphates in nature (geological and biological occurrence) and to underline the peculiar characteristics of nanocrystalline apatites. The aim of the second part is to show the most important analytical techniques for the characterization of apatite features and to describe the new theories behind the apatite crystallization and dissolution processes. The last part describes the traditional and the most exciting and innovative applications of pure, ionic-substituted, and organic-functionalized apatite as biomaterial. The chapters, written by eminent scientists, will serve as an important and useful reference source for a broad audience that consists of both expert (materials scientists, biomedical engineers and biologists) and non-expert readers to who want to improve their knowledge in the field of apatite based biomaterials.