The osteoarthritis disease process affects not only the cartilage but also the entire joint structure, including the synovium, bone and periarticular muscles. Characteristically, abnormal biomechanical forces result in an imbalance between chondrocyte anabolic and catabolic pathways, which ultimately leads to progressive joint destruction. Within cartilage and synovium, pro-inflammatory cytokines, particularly IL-1b and TNF-a, auto-catalytically stimulate their own production and induce chondrocytes to produce additional catabolic mediators, including proteases, chemokines, nitric oxide, and prostaglandins. The success of targeted biological therapy in rheumatoid arthritis has taught that the blockade of a single dominant cytokine can lead to remarkable clinical benefit, even in complex disease. The effectiveness of biologicals in inflammatory arthritides as disease modifying agents has increased the likelihood that similar strategies can be developed to target specific molecular mechanisms in osteoarthritis (OA). However, since the clinical development program for disease-modifying OA drugs (DMOADs) is complicated by the slow progression of disease in many patients, the introduction of DMOADs will be greatly enhanced by advances in imaging and biomarkers that serve as validated surrogate endpoints for meaningful clinical outcomes.