The turbulent flow within a street canyon and the approaching boundary layer has been studied using idealized wind tunnel models and a semi-idealized field experiment conducted in Nantes, France. The effect of upstream roughness on street canyon flow (lateral length/height, L/h = 30) using either 3D (cube) or 2D (rectangular block) upstream roughness, of the same height as the canyon, has been studied for two streamwise canyon width to height aspect ratios (AR) of 1 and 3 using Particle Image Velocimetry. A further wind tunnel model of equivalent geometry to the field experiment was used to compare with flow data obtained using sonic anemometers within the field experiment.  The results show that in both the field and wind tunnel there is a significant influence by the upstream roughness on the flow within the canyon with respect to the turbulence intensities, shear layer size, turbulence spectra and canyon ventilation.