Wilhelm Roentgen’s reported X-rays in 1890. Today, imaging with X-rays is perhaps the most commonly used diagnostic tool with medical profession. X-ray unit is in fact a life line of any working hospital. This chapter carries information on x-rays tube and its maintenance and working of x-ray machine with electric circuit. Further, mechanism of X-rays production, their properties and applications in research and diagnosis has been discussed. Much needed information on the use of X-rays in radiography, fluoroscopy, computed tomography, therapy and molecular structure determination has been analysed in critical manner. The last decade saw an unprecedented increase in the use of x-rays for diagnosis and therapy. The extensive use of x-rays has raised certain questions regarding its safety. To analyse this problem the basic knowledge of x-rays has been reexamined.