The interfacial structure in thin film flow, the large and small waves' characteristics, is modelled and compared with experiment. The modelling of the large waves is based on different physical mechanisms controlling the various zones along the wave. An essential mechanism associated with the large wave motion is periodic distortion of the hydrodynamic wall boundary-layer at the wave front, followed by a recovery process in the wave back. It is shown that sufficient information may be available to generate a closed-form solution. The analysis also suggests that a coupling exists between the small and large waves. The nature of this coupling is introduced in terms of wall-shear relaxation ahead of the large wave front and appears to dominate the characteristics of both classes of waves.