Over the past years, a large number of novel X-ray imaging and data processing methods have been developed. The application areas of X-ray computed tomography (XCT) are highly diverse and extensive, since any material or component may be examined using XCT. The major application areas of XCT in science and industry are found in non-destructive testing, 3D materials characterization, and dimensional measurements (metrology). The nonmedical XCT market is steadily growing, but the full potential of this technique for industrial applications has not been exploited yet. There are many useful XCTapplications which still have to be discovered. This chapter provides an overview of the principles of XCT, of drawbacks such as measurement artifacts as well as their correction, of different XCT methods and scanning protocols, as well as of applications of XCT. The focus of this chapter lies on XCT for materials simulation and high-resolution, quantitative, in situ, and phase-contrast XCT.