Osteoporosis is a major public health problem through its association with fracture. The problem may be alleviated substantially by appropriate early intervention before fracture occurs. This chapter discusses the epidemiology of osteoporosis and addresses the following questions: How should osteoporosis be defined? What is the incidence and prevalence of osteoporosis and fracture? Is there geographical variation in the occurrence of osteoporosis? What are the risk factors for osteoporosis and do they explain the occurrence of osteoporosis and osteoporotic fracture?