The scale of features that control the physical properties of engineered materials is ever decreasing. We can investigate the structure of these materials using several techniques. The techniques are usually selected based on the feature size of interest. Typical scales are the millimeter or optical scale, the micron or microscopic scale, and the nanometer or atomic scale. As the feature size decreases, the capabilities of the technique must increase.

Typical features that require at least microscopic characterization include particles in super alloys, grain misorientations in high temperature superconductors and thin films, inclusions in steels, reaction products in gas chambers.