... Astronomy and Astrophysics, Pennsylvania State University, . ... The application of CCDs to X-ray imaging and spectroscopy for astronomy is described. ... Results of recent research programs to optimize CCD X-ray response are presented. It is shown that very high quantum efficiencies and Fano noise limited energy resolutions can be obtained. A number of issues related to the practical implementation of future instruments are reviewed. ... Contrasting optical and X-ray applications . ...