Bone is a metabolically active organ that undergoes constant remodeling. Bone is very important for maintaining homeostasis of calcium and phosphorous in the body. Disorders of bone metabolism may encompass disease processes involving underactive or overactive bone turnover. The spectrum of abnormal bone metabolism includes rickets and osteomalacia; osteopenia and osteoporosis; osteogenesis imperfecta, renal osteodystrophy; osteopetrosis and osteosclerosis; and effect of pharmacologic therapies on bone metabolism. The recognition, evaluation, treatment, and prevention of these conditions will be discussed after a brief description of normal bone metabolism.