Aspects of Langmuir circulation (Lc) which relate to the dispersion of floating material are reviewed. These include convergence, dispersion by advection (particularly of a plume of floating oil when wind and current are in different directions) and the spread and dispersion by cell instability or breakdown first described by Csanady. There are, however, processes which compete with Lc to diffuse floating material. In shallow tidally mixed seas, where the environmental impact of an oil spill may be greatest, cross-wind dispersion caused by Lc will dominate over that produced by bottom turbulence if the ratio of the wind speed, W, to current, U,is sufficiently large. Observations and rough estimates suggest a transition near W/U = 15. A simple model is devised to estimate cross-wind dispersion in shallow unstratified waters when turbulence generated at a flat seabed dominates that produced by Lc, but when the effects of Lc are still evident in aligning filaments of oil, as may commonly be the case in moderate winds in coastal or continental shelf waters.