High-Resolution X-Ray Spectroscopy with Chandra and XMM-Newton

The launches of the Chandra X-Ray Observatory in June 1999 and the XMM-Newton Observatory in December 1999 opened a new era in X-ray astronomy. Both of these missions incorporate novel diffraction grating spectrometers that are providing the first high-resolution X-ray spectra of most classes of astrophysical sources. The spectra obtained to date exhibit a wealth of discrete detail, yielding sensitive constraints on physical conditions in the emitting plasmas. We review the essential characteristics of these instruments, the basics of X-ray spectral formation in cosmic sources, and the exciting new results that have emerged from Chandra and XMM-Newton grating observations of a wide variety of astrophysical systems.