This chapter provides detail description of Osteoporosis. Chapter has 6 well illustrated diagrams and pictures. Osteoporosis, factors weakening the bone in osteoporosis, criteria for osteopenia and osteoporosis, etiology of osteoporosis, clinical features of osteoporosis, investigations of osteoporosis, quantitative assessment of bone mineral density, drug therapy for osteoporosis, conservative management of vertebral compression fracture, percutaneous intervention for osteoporotic vertebral compression fracture, recommended daily intake of calcium and vitamin D, surgery for osteoporotic compression fracture, recommendations on the methods for internal fixation of the osteoporotic spine are described in detail. 7 tables are included to highlight factors weakening bones in osteoporosis, aetiology, indications, screening, drug therapy for osteoporosis and recommended daily intake of calcium and vitamin D. 86 references are included at the end of the chapter to facilitate further reading.