POROUS inorganic solids find,vide application in, for example, catalysis and separation technologies. One of the most promising routes to such materials exploits cooperative interactions between a supramolecular organic template and inorganic precursor molecules to create an ordered porous solid(1-7). This general approach offers considerable flexibility, and has led to materials with a wide range of bulk morphologies and controlled pore diameters spanning several orders of magnitude(8-10). From a technological point of view, the preparation of such materials in the form of mesoporous thin films is desirable, but attempts to achieve this aim have been largely unsuccessful, resulting in disordered materials(11), Here we report the synthesis of thin (similar to 0.2-1.0 mu m) ordered films of mesoporous silica on freshly cleaved mica substrates. The films are stable on removal from the substrate. We propose a model to explain the formation of these films, in which the surface structure and reactivity of the mica substrate controls the orientation of the micellar precursor species, which in turn imposes order on the resulting solid film.