Bone and teeth are mineralized skeletal elements, composed principally of calcium and phosphate. Bone is metabolically active and continuously replaced by bone remodeling. The latter progresses through bone resorption and bone formation in a coordinated manner. Imbalance of bone resorption and bone formation may lead to osteoporosis, a loss of bone mass and strength. Unlike bone, teeth are less metabolically active, resorbed only during replacement in physiological conditions. Yet the superficial layer of enamel repeats demineralization and remineralization. If demineralization dominates remineralization in enamel, dental caries occur. High rates of bone remodeling are essential for the homeostasis of calcium and phosphate. In addition to bone remodeling, calcium and phosphate homeostasis is maintained by the absorption of calcium in the small intestine and reabsorption or excretion of calcium and phosphate in the kidney. In these processes, responses to a change in calcium or phosphate concentration in the extracellular fluid are mediated largely by the parathyroid hormone secreted by the parathyroid glands, vitamin D activated in the kidney, and fibroblast growth factor 23 secreted by osteocytes in bone. The homeostasis of calcium phosphate is thus maintained by the interplay of bone, parathyroid glands, small intestine, and kidney.