This report describes an experimental investigation of the effects of nozzle exit boundary layer conditions on turbulent mixing in free jets. Mean velocity and turbulence measurements were obtained in flow fields produced by several axisymmetric and two dimensional nozzles with exit velocities in the range of 30 to 800 ft/sec. With tripped turbulent initial boundary layers, spatial mixing rates were found to be independent of jet exit velocity, the mean flow fields scaled with nozzle exit dimensions, and the same results were obtained with different air supply facilities. With laminar and transitional initial nozzle boundary layers the core lengths were found to be unpredictable, showing large changes with both nozzle exit dimensions and velocity, and displaying a strong dependence on air supply facility characteristics. A clear conclusion from our investigation was that in experimental testing of models that incorporate free jets the nozzle wall boundary layer must be turbulent to eliminate a frequent source of poor agreement between model and full scale hardware performance. (Author).