The Chandra X-ray telescope has four separate detectors, two charge coupled devices, and two microchannel plates, behind a set of four highly polished, nested mirrors. The on-orbit performance of the imaging system is ≪1 arcsec, a dramatic improvement from the 5–8 arcsec previously available. In addition, two transmission gratings can be placed in the system, which for point sources can reach resolutions of 300–1000+ over the range λ∼1.5–160 Å. The entire system was calibrated prelaunch at NASA/MSFC in Huntsville, Alabama. The results have been dramatic: the first light image of the supernova remnant Cas A showed a never-before-seen point source near the center of the remnant that may be the neutron star left over after the explosion. Even the calibration image of a distant quasar (taken for focusing purposes) showed an x-ray emitting jet extending out from the nucleus for more than 20 kpc, which challenges current theories about jet propagation. The grating observations done by Chandra take x-ray astrophysics out of the photometry era into the spectroscopic age. Astrophysical plasmas reach conditions far out of the reach of any terrestrial laboratory, and astronomers are just beginning to understand the diagnostics of these plasmas; Chandra observations may even someday provide the best measurements of certain atomic rates. However, before that point is reached the astronomical community must gain a much better understanding of the existing and ongoing work in x-ray diagnostics from other fields. The general state of x-ray diagnostics for astronomical plasmas will also be discussed. © 2001 American Institute of Physics.