This chapter discusses the definition, epidemiology, risk factors, primary and secondary prevention, treatment and evaluation of osteoporosis (OP). OP is common and its incidence increases with age. The prevalence of OP in women age 50 to 54 in the UK is between 2 and 3.5%. After menopause, a woman's rate of bone turnover and loss of bone mass increases precipitously. Smoking cigarettes, high caffeine intake, and excessive alcohol use increase the risk of osteoporosis. Hormone replacement therapy in postmenopausal women is protective against the development of OP, helps reverse the bone loss, treats osteoporosis and prevents fractures. Dual-energy X-ray absorptiometry (DEXA) scan is the most precise and common test used to detect bone density. Treatment of OP includes lifestyle changes and pharmacological therapy. Normal postmenopausal bone loss is 2% per year. A woman with OP should be started on lifestyle changes and pharmacotherapy.