Cone beam computed tomography (CBCT) is a versatile tomographic X-ray imaging modality that utilizes two-dimensional (2D) area detectors to acquire X-ray projection images around a three-dimensional (3D) object. The name of “cone beam” is in contrast to the traditional “fan-beam” geometry of clinical computed tomography (CT) systems, which typically collimate the X-ray beam into a relatively narrow slit (see Section III, Chapter 32). Thus, the acquisition process of CBCT is very similar to X-ray fluoroscopy (see Section II, Chapter 21), except that the X-ray tube and the area detector rotate around a common isocenter during the 714exposure. Cone beam CT systems normally do not require a complicated mechanical gantry as in a clinical CT scanner and are, therefore, much easier (and cheaper) to build. More importantly, due to the large coverage area of the 2D area detector, a single rotation will be sufficient to image a certain sized volume (such as an entire organ). This avoids the synchronized rotation with table increment (the helical scan) and reduces the potential of object motion during the acquisition. Other key advantages of CBCT when comparing to fan-beam CT include the better in-plane spatial resolution and naturally iso-tropical resolution in 3D. Given its flexibility and acquisition efficiency, CBCT has emerged as one of the most widely utilized modalities throughout the entire field of biomedical imaging and non-destructive evaluation (NDE) (see Section III, Chapter 45). In this chapter, we will first introduce the development of cone beam CT and the basic concept of CBCT data acquisition and image reconstruction. Then the focus will be on its broad application spectrum and technical issues related to image quality and radiation dosimetry. We will also cover the major challenges and technical keys related to CBCT. Future directions will be reviewed at the end of the chapter.