Articular cartilage is a thin (about 1–6 mm in human joints) layer of fibrous connective tissue covering the articular surfaces of bones in synovial joints. It consists of cells (2–15% in terms of volumetric fraction) and an intercellular matrix (85–98%) with a 65–80% water content. Articular cartilage is a viscoelastic material and in conjuction with synovial (joint) fluid, allows for virtually frictionless movement (coefficients of friction from 0.002–0.05) of the joint surfaces. Osteoarthritis is a joint disease that is associated with a degradation and loss of articular cartilage from the joint surfaces and a concomitant increase in joint friction causing pain and disability, particularly in the elderly population. The primary functions of articular cartilage include force transmission across joints, distribution of articular forces so as to minimize stress concentrations, and provision of a smooth surface for relative gliding of joint surfaces. In most people, articular cartilage fulfills its functional role for decades, although the incidence of osteoarthritis in North America is about 50% among people of age 60 and greater.