This chapter discusses the frontier of the electromagnetic spectrum: x-ray radiation. Radiographs – x-ray images colloquially called “x-rays” – are two-dimensional shadow images created on photographic films by x-rays whose energy has been partially absorbed by the body organs and tissues. X-ray images are formed on photographic films or in digital detectors by highly penetrating rays of electromagnetic radiation transmitted through the body. In medical physics, the term x-ray is generally used to characterize such photons when they are generated in a continuous spectrum of energies by a device, while photons of specific energies generated by radioactivity are called gamma rays. The way x-rays are generated plays a major role in determining the quality and characteristics of the resulting images. In general, electromagnetic waves are emitted by electric charges when they undergo a change in motion. X-rays are produced when accelerated electrons collide with the atoms of the anode.