Air-water bubbly flows are encountered in numerous engineering applications. One type of air-water shear flow, the developing flow region of a plunging jet, is discussed in the light of new experimental evidence. Distributions of air concentration and mean air-water velocity, and bubble chord length distributions are presented for inflow velocities ranging from 2 to 8 m/s. The results indicate that the distributions of void fraction follow closely analytical solutions of the diffusion equation, as developed by Chanson (1995a Report, CH46/95, pp. 368, 1997 Report CH48/97). In air-water shear layers, the velocity distributions have the same shape as in monophase flows but the characteristic parameters of the shear layer differ from monophase flow results, because of the interactions between the entrained air bubbles and the turbulence.