A review is provided of stably stratified towing-tank experiments on plume behavior in complex terrain. Recent studies have shown that stratified towing tanks are useful tools to enhance basic physical understanding of transport and diffusion of pollutants over complex terrain as well as to provide practical guidance or 'rules of thumb' for locating sources and estimating likely impacts of sources in complex terrain. The concept of a dividing-streamline height, derived from towing-tank studies, provides a useful interpretation of strongly stratified flows. The dividing streamline forms the boundary between a lower layer of essentially horizontal flow and an upper layer that passes over the hill top. Plumes released in the lower layer impact on the hill surface, with resulting surface concentrations essentially equal to those observed at the center of the plume in the absence of the hill. A plume released in the upper layer can be treated as a release from a shorter stack upwind of a lower hill, i.e., as if a ground plane were inserted at the dividing-streamline height. Strongly stratified towing-tank experiments on flows over two-dimensional ridges were found to have no counterpart in the real atmosphere because of the unsteadiness created by the finite length of the tank.