X-Ray Astronomical Instrumentation.- Overview.- Proportional Counters.- Scintillation Counters.- Imaging Proportional Counters.- Aperture Modulation Telescopes.- Wolter Optics.- CCD Detectors.- High Resolution Spectroscopy.- Galactic X-Ray Astronomy.- Solar System Objects.- Nuclear Burning Stars.- White Dwarfs.- X-Ray Emission of Cataclysmic Variables and Related Objects.- Classical Novae.- Pulsars and Isolated Neutron Stars.- Accreting Neutron Stars.- Black-Hole Binaries.- X-Ray Studies of Supernovae and Supernova Remnants.- The Interstellar Medium.- The Galactic Center.- Extragalactic X-Ray Astronomy.- X-Rays from Nearby Galaxies.- X-Ray Flares in the Cores of Galaxies.- Active Galactic Nuclei.- X-Ray Studies of Clusters of Galaxies.- Gamma-Ray Bursts.- Cosmic X-Ray Background.- The Future.