This chapter gives an overview on osteoarthritis (OA). OA is the most common joint disease, affecting 80% of people over age 50. OA is a degenerative joint disease that stems from loss of joint protective structures; often cartilage fibrillation and catabolism or ligamentous injury initiate the cascade of accelerated joint wear. Clinical evaluation includes plain radiographs, which almost always show joint space narrowing. Osteophytes, subchondral cysts, and osteosclerosis may also be seen. Nonsteroidal anti-inflammatory drugs (NSAIDs) and acetaminophen are the mainstays of OA pharmacotherapy. Surgery can provide dramatic pain relief. Restoration of stability through ligament grafting slows OA progression. Hip and knee replacement procedures generally have good success, and multimodal analgesia can reduce the chance of postoperative chronic pain.