Osteoarthritis (OA) is a joint disease that most commonly affects middle-aged and elderly people. As the prevalence of OA is expected to increase substantially in the future, a clearer insight into the risk factors for disease development and disease in progression is desirable. In this Review, we summarize the evidence available from systematic reviews regarding the determinants of the development and progression of hip and knee osteoarthritis (OA). There is moderate to strong evidence that physical workload (in hip and knee OA), high-intensity sporting activities (in hip OA), and being overweight (in clinical hip OA) are risk factors for OA. There is also moderate to strong evidence that having OA and a high serum level of hyaluronic acid are prognostic factors for knee OA. In addition, there is strong evidence that superolateral type of migration of the femoral head and atrophic bone response are prognostic factors for hip OA. Further research into the identification of prognostic risk factors for symptomatic progression of knee OA is warranted.