Computed tomography (CT) with X-rays is widely used in medicine and nondestructive testing today. However, in process applications, X-ray tomography has so far been more seldom used, obviously due to its high complexity and costs. Nonetheless, particularly in laboratory studies, it has frequently proven its superior capability to measure multiphase flow parameters, such as local phase fractions in pipes, vessels, or other process system components, with high resolution and accuracy. Most recently, different technologies were presented that allow faster tomographic imaging of flows with X-ray CT, which now opens the door for a wider application of this technique in process analysis, monitoring, and control. This chapter gives a concise overview of basic principles and hardware of X-ray CT, particularly with respect to process applications, and provides state-of-the-art examples of its application in multiphase flow analysis.