Knee osteoarthritis (OA) is a highly prevalent and disabling disease. Most persons age 45 and over with chronic knee pain have OA and with characteristic history and physical findings, diagnostic imaging is usually not necessary. Further, treatment of chronic knee pain with or without evidence of OA is similar, so imaging does not usually alter therapy. The exception is atypical presentations, such as sudden onset of pain perhaps after trauma or evidence of arthritis in atypical locations elsewhere in the body. Imaging is also unnecessary to follow patients. Given the absence of treatments that slow progression, there is little rationale for acquiring repeated imaging. However, ultrasound or other knee imaging may be helpful in locating the joint when carrying out intraarticular corticosteroid injections. There is controversy as to whether imaging should be acquired before these injections, but recent studies suggest no increased risk of disease progression for most persons receiving these injections. While guidelines currently discourage imaging in the diagnosis or management of most persons with OA, this may change for individuals with identifiable correctible lesions, when effective treatments that alter progression emerge or when imaging is used to identify subtypes of disease that may respond to specific treatments.