A semi-empirical analysis is developed for the over-all flow pattern of subsonic turbulent flow over backward facing steps. Good agrement is found between theory and experiment for the prediction of two-dimensional reattachment length for small values of step height to throat width ratio; an asymptotic solution for large values of step height is also given and discussed. Mean velocity profiles calculated by the present analysis are shown; they require an empirical fit at one point. Good agreement with experiment is found in the region near the step face, but agreement is poor near the reattachment region. Experimental results are represented for flow patterns over backward facing steps covering a wide range of geometric variables. Velocity profile measurements are given for both single and double steps. The stall region is shown to consist of a complex pattern involving three distinct regions. The double step contains an asymmetry for large expansions, but approaches the single-step configuration with symmetric stall regions for small values of area ratio. No effect on flow pattern or reattachment length is found for a wide range of Reynolds numbers and turbulence intensities, provided the flow is fully turbulent before the step. (Author).