Articular cartilage is a complex tissue maintained by chondrocytes, which undergo metabolic changes as a result of aging, disease, and injury. These changes may hinder tissue maintenance and repair, resulting in accelerated loss of articular surface and leading to end-stage arthritis. Researchers are investigating both normal and pathologic cellular and molecular processes as well as the development of chondroprotective agents to improve the metabolic function of articular cartilage. Current research is helping to clarify the mechanisms by which a variety of agents, such as glucosamine, chondroitin sulfate, hyaluronic acid, green tea, glucocorticoids, and nonsteroidal anti-inflammatory drugs, can modify the symptoms and course of osteoarthritis. Also under investigation are methods of stimulating repair or replacing damaged cartilage, such as matrix metalloproteinase inhibitors, gene therapy, growth factors, cytokine inhibitors, and artificial cartilage substitutes. Tissue engineering, the combining of artificial matrices with cells and growth factors or genes, offers great potential for improving patient care.