Osteoarthritis can be viewed as the clinical and pathological outcome of a range of disorders that results in structural and functional failure of synovial joints. Osteoarthritis occurs when the dynamic equilibrium between the breakdown and repair of joint tissues is overwhelmed. Structural failure of articular cartilage can result from abnormal mechanical strains injuring healthy cartilage as well as from failure of pathologically impaired cartilage degenerating under the influence of physiological mechanical strains. Primary and secondary subsets of OA and defined but in the majority of cases the pathogenesis is multifactorial, involving environmental as well as genetic factors. The influence of occupational factors, body weight, trauma and recreational activities are briefly reviewed, as are the role of developmental abnormalities, collagen gene mutations, denervation of joints and inherited and acquired erros of metabolism.