The principle of the tomography technique and the different possible set-ups, which can be used to obtain medium-(10 lm) and high(1 lm) resolution, three-dimensional, non-destructive images, are shown in this paper. Illustrations are made of the applications of the technique in the field of materials science. Examples are given for medium-resolution images of metallic foams and model metal matrix composites that are reinforced with spherical particles. High-resolution examples are shown for aluminium alloys. For low-absorbent materials we show that the phase contrast obtained using synchrotron radiation can provide a valuable solution. The quantitative use of these images, coupled with in-situ tensile tests or used for the simple analysis of the initial microstructure of several structural materials, is also described.