Abstract Clay-based polymer nanocomposites have become technologically relevant materials in recent years, ( Alexandre and Dubois, 2000 ; Pinnavaia and Beall, 2000 ; Ray and Okamoto, 2003 ; Ahmadi et al. , 2004 ; Becker and Simon, 2005 ) and they are likely to remain of fundamental interest to the scientific community for the foreseeable future. The variations of polymer matrix material, layered silicate, organic modifier, processing parameters and characterization methods, leave endless combinations for study. While some general rules have begun to emerge, the field is still lacking a broad description of the processing - morphology - properties relationship. The critical link in this relationship will be the ability to accurately characterize the morphology of polymer nanocomposites in a quantitative manner. Traditionally these materials are characterized in a qualitative fashion, and so the ability to link the morphology to a quantitative property has not been definitive. Having said this, quantitative nanocomposite morphology characterization is by no means a simple task - it will take a detailed comparison of several complimentary techniques, as well as comparison with several measured properties before the structure-properties relationship begins to mature. Nanocomposites have a hierarchical structure, and therefore a description of the microstructure at one length scale is not sufficient in many cases. Most schematics depicting morphology in nanocomposites (phase separated, intercalated or exfoliated) are grossly simplified, as well-defined structural variations can exist from the nanometer scale to the several micron scale and to the millimeter scale. Furthermore, the standard definitions of