A direct, simple, and accurate way to measure skin friction by oil-film laser interferometry has been developed by various researchers. Equations and methods were developed to correct measurement errors arising from three-dimensional effects and pressure gradients. The oil-film, dual-beam laser interferometer was constructed to measure the skin friction around a wing-body junction in a three-dimensional, turbulent boundary layer with pressure gradients. The flow was dominated by the formation of a junction vortex generated at the nose of the wing-body. The oil-film skin friction results were compared with previous skin-friction measurements for the flow obtained by hot-wire measurements. The skin friction values agreed within approximately 8% between the two methods. The effects and benefits of scanning laser interferometry and alternative beam directions were investigated and discussed. The effect of dirt contamination on the data is also discussed. Methods to improve the data quality are presented. / Master of Science