Mucinous glycoproteins, such as lubricin play a prominent role in the boundary lubrication mechanism in diarthrodial joints. Although many studies have tried to elucidate the lubrication mechanisms of articular cartilage, the molecular details of how lubricin interacts with cartilage surfaces and mediates their interaction still remain poorly understood. Here we used model substrates, functionalized with self assembled monolayers (SAMs) terminating in hydroxyl or methyl groups, (1) to determine the effect of surface chemistry on lubricin and hyaluronic acid (HA) adsorption using surface plasmon resonance (SPR), and (2) to study normal force interactions between these surfaces as a function of lubricin and HA concentration using colloidal probe microscopy. We found that lubricin is amphiphilic and adsorbed strongly onto both methyl and hydroxyl terminated surfaces. On hydrophobic surfaces, lubricin likely adopts a compact, loop-like conformation, in which its hydrophobic domains at the N- and C-terminus serve as surface anchors. On hydrophilic surfaces, lubricin adsorbs anywhere along its hydrophilic central domain and adopts, with increasing solution concentration, an extended, tail-like conformation. Overall, lubricin develops strong repulsive interactions, when compressing two surfaces into contact. Furthermore, upon surface separation, adhesion occurs between the surfaces, due to molecular bridging and chain disentanglement. This behavior is in contrast to that of HA, which does not adsorb appreciably on either of the model surfaces, nor does it develop significant repulsive interactions. Adhesive forces particularly between the hydrophobic surfaces are large and not appreciably affected by HA. For a mixture of lubricin and HA we observed slightly larger adsorptions and repulsions than those found for lubricin alone. Our experiments suggest that this interaction depends on unspecific physical rather than chemical interactions between lubricin and HA. We speculate that in mediating interactions at the cartilage surface, an important role of lubricin, possibly in conjunction with HA, is one of providing a protective coating on cartilage surfaces that maintains the contacting surfaces in a sterically repulsive state.