Summary: If a sharp edge occurs in a reflector, the wavefield predicted by geometric ray theory shows shadow boundaries between illuminated zones and shadow zones. One may correct for these discontinuities in the wavefield by adding edge waves. In this paper the edge wave is analysed as a solution of a parabolic differential equation that describes transverse diffusion between the illuminated zone and the shadow zone across the shadow boundary. Here, the edge wave is described constructively in terms of dynamic ray tracing, thereby indicating how it can be implemented in a ray tracing program when the latter is equipped with the facility of dynamic ray tracing.