Osteomalacia, osteopenia, and osteoporosis are distinct bone diseases each with characteristic pathogenesis, risk factors, and aetiologies. Osteomalacia is a disease of defective bone mineralization of osteoid and impaired remodelling at sites of bone turnover. It occurs chiefly due to vitamin D deficiency, inadequate serum and extracellular levels of essential minerals for bone growth (particularly calcium and phosphate), alteration in pH (such as in renal tubular acidosis, chronic kidney disease, and metabolic acidosis), or administration of direct mineralization inhibitors such as etidronate, aluminium, or fluorides. Osteoporosis is characterized by reduced bone mass either due to decreased remodelling or excessive resorption. The main pathogenesis of osteoporosis is defective development of normal bone density due to reduction of the sex hormone influence on bone development. The main causes of osteoporosis are hypogonadism, androgen insensitivity syndromes, and delayed puberty. Other risk factors include excessive alcohol consumption, heavy smoking, low body mass index, low levels of physical activity, vitamin D deficiency, hypercalciuria, diabetes mellitus, cerebrovascular stroke, history of bone fractures, hemochromatosis, anorexia nervosa, growth hormone deficiency, chronic steroid use, and antiepileptic drugs (e.g. phenytoin). Osteopenia is considered a precursor to osteoporosis or a less severe form of osteoporosis. It has almost the same pathogenesis, aetiology, and risk factors of osteoporosis. This article will address the differences between osteomalacia, osteoporosis, and osteopenia as regards the pathogenesis, risk factors, and causes. Keywords: Osteomalacia, osteopenia, osteoporosis.