Osteoporosis is a common bone disease that will be frequently encountered by physical therapists. Characterized by low bone mass and microarchi‐tectural changes that increase the susceptibility to fracture, approximately 30 million postmenopausal women in the United States have either osteoporosis or osteopenia, and the incidence is likely to increase with the aging of the population. Physical therapists need to be aware of osteoporosis and its consequences. Modifiable risk factors represent an opportunity to intervene and help young women develop healthy bones long before osteoporosis develops. Therefore, this paper will address the epidemiology and demographics of osteoporosis including known risk factors. Normal physiologic development of healthy bone will be presented as a precursor to discussion of the pathphysiology of the osteoporosis disease process.