Synopsis Although osteoarthritis (OA) has traditionally been considered a disease of older age, hip and knee OA can and does affect younger adults, with a profound impact on psychosocial well-being and work capacity. Obesity and a history of traumatic knee injury (eg, anterior cruciate ligament rupture and/or meniscal tear) are key risk factors for the accelerated development of knee OA, while structural hip deformities (including those contributing to femoroacetabular impingement syndrome) are strong predictors of early-onset hip OA. In view of these associations, rising rates of obesity and sports injuries are concerning, and may signal a future surge in OA incidence among younger people. Assessment of hip and knee OA in younger people should focus on a patient-centered history, comprehensive physical examination, performance-based measures, and patient-reported outcome measures to enable monitoring of symptoms and function over time. Referral for imaging should be reserved for people presenting with atypical signs or symptoms that may indicate diagnoses other than OA. Nonpharmacological approaches are core strategies for the management of hip and knee OA in younger people, and these include appropriate disease-related education, activity modification (including for work-related tasks), physical therapist- prescribed exercise programs to address identified physical impairments, and weight control or weight loss. High-quality evidence has shown no benefit of arthroscopy for knee OA, and there are no published clinical trials to support the use of hip arthroscopy for OA. Referral for joint-conserving or joint replacement surgery should be considered when nonpharmacological and pharmacological management strategies are no longer effective. J Orthop Sports Phys Ther 2017;47(2):67-79. doi:10.2519/jospt.2017.7286.