The Osteoarthritis Initiative (OAI) is a large, ongoing research study that aims to improve the prevention and treatment of osteoarthritis. It was launched in 2002 by the National Institutes of Health (NIH) and other organizations to gather data on the natural history of knee osteoarthritis. The OAI collects clinical, radiographic, and MRI data from over 4,700 participants in order to better understand the development and progression of osteoarthritis, as well as identify risk factors and improve diagnostic techniques. The results of this study are intended to inform future research and interventions for individuals with osteoarthritis.