This feature article summarizes recent advances in an emerging three-dimensional (3D) imaging technique, transmission electron microtomography (TEMT), and its applications to polymer-related materials, such as nanocomposites and block copolymer morphologies. With the recent developments made in TEMT, it is now possible to obtain truly quantitative 3D data with sub-nanometer resolution. A great deal of new structural information, which has never been obtained by conventional microscopy or various scattering methods, can be directly evaluated from the 3D volume data. It has also been demonstrated that, with the combination of TEMT and scattering methods, it becomes possible to study structures that have not yet been characterized. The structural information obtained from such 3D imaging provides a good opportunity not only to gain essential insight into the physics of self-assembling processes and the statistical mechanics of long chain molecules, but also to establish the "structure-property" relationship in polymeric materials. (C) 2008 Elsevier Ltd. All rights reserved.