X-rays are produced when the fast moving electrons are stopped by mean of a target material. During this, its kinetic energy is converted into electromagnetic energy which is known as X-rays. The basic requirements of X-ray production are electron source (cathode), anode (on which electrons are stopped), high voltage supply to accelerate the electrons, vacuum, tube insert and housing. The electrons are produced by thermionic emission or by the ionization in gas. The cathode acts as electron source and the anode act as a target source. The high voltage is supplied between the cathode and anode and this voltage is used to accelerate the electrons to a high velocity, as a result the electrons will possess the high kinetic energy. A high vacuum is maintained between the cathode and anode .this is necessary to avoid the collision between electrons and gas molecules and to avoid the oxidation of tungsten filament in the cathode. The required vacuum is less than 10 mmHg. The housing absorbs the x rays emerging in undesired directions, maintain the require vacuum and also contains the cooling system which removes the heat from the target. The equipment having all the above requirements is called an x –ray tube.