This document provides an overview of osteoarthritis of the knee. It defines osteoarthritis as a non-inflammatory degenerative joint condition. It describes the pathology and changes that occur in the articular cartilage, bone, synovial membrane, capsule, ligaments and muscles. Risk factors, clinical presentation, diagnostic tests including x-rays and MRI, and grading scales are outlined. Both non-surgical and surgical treatment options are discussed including exercises, braces, medications, injections, osteotomies and knee replacements.