Zeolites are crystalline aluminosilicates with frameworks built from corner-sharing TO4- tetrahedra(where T is Si or Al but can also be substituted with P, Ga, Ge, etc.) to produce channels or cavities of molecular dimensions. Owing to these characteristic features, zeolites have attracted much attention not only for catalytic applications but also as containers of confined materials. In most circumstances zeolites can only be synthesized as fine powders, ca. 1 μm, and the additional presence of defects or intergrowths makes structure solution difficult. HREM is therefore one of the most important tools for the investigation of such structures and the early work of Thomas and his group in Cambridge were dedicated to developing such techniques. The advantage of HREM has been subsequently demonstrated especially for characterizing and determining fine structures, e.g. (i) zeolite intergrowths structures such as ERI/OFF and FAU/EMT, (ii) enantiomeric intergrowths of structural units in ETS-10 and structural solution, (iii) surface structures and growth units and (iv) size of clusters and their registry with the framework structures.