An apparatus has been designed and constnlcted for the study of liq.uic1 film flow on flat surfaces of varioue inclinations with and without a counter-flow of gas. Experimental results ho.ve b-:~en obtained for the system water-air at chamJ.el slopes of 7?t° to 900 on the Im an film thickness, the velocities and wavelengths of the interfacial waves, the s urf2.ce velocity and wall shear-stress in the film, all as functions of the channel slope ~d the liquid and gas flow rates. Velocity profiles, wall and interfacial shear-stresses, and static pressure drops of the gas stream have been measured at 43 0 slope as functions of gas and li~uid flow rates and position along the channel. Numerous visual and photo0raphic obse_vat~ollS m the flow behaviour have been made, together V the cine--photographs for investigating mixing in the wave fronts. Theoretical calcu1ntions have l)een made of' the surface- tension edbe effect; the results ~re in moderate agreement will the experiments. The experimental results have been compared with published theories and data. The usual theories of wavy film fJ. OVJ have been found to be Applicable only at very low flow rates. It has been shown that the complex phenomena occuring in film flow can be represented on a lle-J?r-We network, and a systematic nomenclatu::ce has been proposed for the flow regimes The importance of the gas entry effect in calculatinG two-phase flows of the plesent type has been demonstrated, and both the liquid entry zone and the surface tension ed~e effect may have an important influence on mass transfer in film-type equipment.