Osteoarthritis is the most common form of arthritis and is a leading cause of disability in the elderly. Given the anticipated increase in osteoarthritis prevalence, the need to identify risk factors for incident osteoarthritis, osteoarthritis progression, osteoarthritis-associated physical function decline, and disability is an especially high priority. Findings have implicated several factors, including genetic factors, aging, joint deformity and injury, obesity, and hormonal deficiencies in the pathogenesis of osteoarthritis. Recent studies have identified risk factors associated with progression of the disease including varus-valgus alignment, bone marrow edema lesions, varus thrust, a reduced hip abduction moment, and obesity. Predictors of function decline in osteoarthritis include lower self-efficacy, knee laxity, less aerobic exercise, worse joint proprioception, and greater knee pain.