This review has shown that osteoporosis is a major public health problem because of its association with fracture. It is now possible to predict future risk of fracture by measuring BMD with noninvasive techniques. The relation between BMD and fracture is comparable to that between blood pressure and stroke such that fracture risk can be assessed from a definition of osteoporosis using bone mass and past history of fracture. Because some of the risk factors for peak bone mass, involutional bone loss, and fracture are now characterized, coupled with innovative agents capable of retarding bone loss, it is becoming possible to generate preventive strategies, for the entire population as well as for those at highest risk.