Zeolites have been recognized as 3D framework materials but are now known to also exist in various 2D layered forms with sheets of one unit cell or smaller thickness. We propose a classification system and an expanded concept of zeolite structures integrating various 2D and the traditional 3D forms. Zeolite topology is defined as the primary structure. Various kinds of zeolite mono-layer assemblies are secondary structures. Based on the literature 15 distinct layered forms are recognized. A detailed table is generated showing layered forms that have been reported for various topologies. It provides a classification tool for recognition and verification of known materials. It may be used to identify unknown ones of particular interest to pursue. (C) 2013 Elsevier B.V. All rights reserved.