Calcium and vitamin D are both of key importance for bone health, and their effects on bone appear to begin even in utero and continue throughout life. The dietary requirements for both calcium and vitamin D are different at different stages of the lifespan. Importantly, in Australia the bulk of vitamin D comes from manufacture of vitamin D in the skin from ultraviolet light exposure i.e. from sun exposure, as the amount of vitamin D in foods is low. Vitamin D deficiency is common at all stages of life and some groups are at particularly high risk. Adequate calcium intake and maintaining adequate vitamin D levels are important in childhood for maximising peak bone mass, but the effect of calcium supplementation on bone mineral density is small. The role of vitamin D supplementation in childhood outside of treating rickets is unclear, though there is potential for a clinically significant effect. Calcium and vitamin D supplements have been investigated for the primary prevention of osteoporotic fracture in the elderly. Calcium and vitamin D is effective at reducing non-vertebral and vertebral fractures in the institutionalised elderly but community-based studies show conflicting results. There is no evidence that calcium, vitamin D or the combination of calcium and vitamin D alone prevent fractures in those who have already sustained a low trauma fracture (secondary prevention) but calcium and vitamin D are both important adjunctive treatments in established osteoporosis i.e. in combination with other pharmacotherapies.