Osteoporosis is the commonest bone disorder in Western populations. It is characterized by low bone mass and microarchitectural deterioration of bone tissue, which lead to increased bone fragility and the potentially devastating consequences of fragility fracture. It has been estimated that at age 50 the remaining lifetime risk of fracture at the wrist, spine or hip is 39% among women and 13% among men. The chapter also explains preterm delivery and bone metabolism; an infant born before 37 weeks of completed pregnancy is by definition preterm. With modern neonatal intensive care, survival is possible after as little as 23 weeks gestation. Preterm infants are born during an extremely rapid phase of mineral accretion and have low skeletal mineral stores at birth compared to a term infant that has built up large stores of mineral during the last trimester, and receives sufficient mineral substrate after delivery for the needs of normal growth and development to be satisfied. The preterm infant differs in a number of ways that renders them susceptible to mineral deficiency and metabolic bone disease: born during a phase of rapid growth and mineral accretion, poor early nutrition/mineral intake, and many more.