Synchrotron x-ray microtomography is a characterization technique increasingly used to obtain 3D images of the interior of optically opaque materials with a spatial resolution in the micrometer range. As a nondestructive technique, it enables the monitoring of microstructural evolution during in situ experiments. In this article, examples from three different fields of metals research illustrate the contribution of x-ray tomography data to modeling: deformation of cellular materials, metal solidification, and fatigue crack growth in Al alloys. Conventionally, tomography probes the 3D distribution of the x-ray attenuation coefficient within a sample. However, this technique is also being extended to determine the local crystallographic orientation in the bulk of materials (diffraction contrast tomography), a key issue for the modeling of microstructure in metals.