This book introduces recent advances in understanding the crystal structure of carbonate hydroxylapatite (also known as bone mineral), which forms the hard tissue of bones and teeth. Bone mineral is the reservoir for carbon dioxide in the body and maintains the concentration of mineral ions in body fluids at homeostasis. The detailed structure of bone mineral has remained obscure more than 80 years after publication of the basic apatite structure, because of the nanoscale size and poor quality of bone mineral crystals. An entirely new approach to the determination of carbonate apatite structures has resulted in a greatly expanded role for the c-axis channel of bone mineral crystals in the control of metabolic acidosis and blood pH. The book includes chapters on apatite mineralogy and geochemistry, synthesis methods, x-ray structure, infrared spectroscopy, crystal chemistry of carbonate hydroxylapatite, and biological apatites. There are 74 illustrations, 25 tables of data, and 3 appendixes. Discussion of the new research is supported by an outline of the theory behind the methods of investigation and reviews of previous research on hydroxylapatite materials, for the benefit of non-specialist students and researchers.