Recent dynamical studies and satellite observations have demonstrated the existence of filamentary structures in chemical tracer fields in the stratosphere. It is evident that the transverse scale of such features is often shorter then the grid spacing of the highest resolution Eulerian models that have been thus far employed. These observations have motivated the development of a novel transport model (CLaMS) that is based on a Lagrangian formulation of the transport of tracers and a mixing algorithm where the intensity of mixing is related to the local fluid straining rates. The motivation for the development of ClaMS will be discussed and the novel components of the model transport scheme will be described. Case studies will be presented using satellite data that illustrate the satisfactory performance of the advection/mixing scheme employed.