Total hip arthroplasty (THA) has become an extremely successful surgical procedure in the past 50 years. It has greatly improved the quality of life of patients. However, there remain clinical concerns. Total hip arthroplasty constructs are sophisticated tribological bearings, made of materials such as cobalt-chrome and ceramic. Advances in materials and design have allowed industry to provide hard-on-hard bearings such as metal-on-metal and ceramic-on-ceramic devices to the market. These sophisticated tribological bearings require advanced mathematical models and experimentation techniques to better understand and predict performance.  In an attempt to more fully understand the behavior of these engineered THA bearing surfaces, thorough literature review was conducted of in vitro wear simulation testing, analyses of retrievals, and clinical assessment of these devices. This information has been combined with further experimental in vitro wear simulations and theoretical analyses.  The experimental in vitro wear simulations and theoretical analyses of this dissertation sought to provide further understanding of the fluid film lubrication of the bearing. This was done through several assessments. The protocols employed in the experimental in vitro wear simulations correspond reasonably with clinical and other published data, however, do not provide delineation of wear performance between THA and resurfacing designs as might be expected. To advance these designs, further experimental development is required. Additionally, data indicates that inclusion of micro-separation in the protocols more closely replicates in vivo use, and should always be included. Contact mechanics of these bearings confirmed that careful selection of design parameters, such as material, diameter, clearance, and surface roughness is needed in the design of the bearings in order to balance the magnitude and distribution of the contact pressure between the articulating surfaces, with surface roughness identified as a primary driver of film parameter and clearance as a primary driver of film thickness. Finally, using wear equations and film parameter estimations, wear factor as a function of film parameter was calculated, resulting in distinct regions for particular bearing technologies, providing initial data for establishing formulas to calculate wear factor values for these bearings.