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Lubrication of cartilage involves a variety of physical and chemical factors, including lubricin, a synovial glycoprotein shown to be a boundary lubricant. It is unclear how lubricin boundary lubricates a wide range of bearings from tissue to artificial surfaces, and if the mechanism is similar for soluble and bound lubricin. The objective of this research was to investigate lubricin as a mediator of articular cartilage boundary mode frictional properties. The central hypothesis of this dissertation was that the boundary mode friction coefficient is mediated by localization of lubricin at the tissue surface. In order to determine the frictional properties of cartilage, a linearly oscillating cartilage-on-glass friction apparatus was designed and validated, and a novel extension of the Stribeck curve, a ‘Stribeck surface, ’ was created to map cartilage lubrication modes. The first aim identified the ability of exogenous lubricin to lubricate articular cartilage and characterized the differential roles of bound and soluble lubricin. The second aim investigated the ability of endogenously synthesized lubricin to lubricate cell-alginate constructs generated from chondrocytes, meniscal fibrochondrocytes, and mesenchymal stem cells. The last aim determined the functional effects of short ter