  The R~300-1000 grating spectra from XMM-Newton and Chandra are a radical
advance, allowing spectroscopic physics techniques to be applied to X-ray
astronomy, revolutionizing a wide range of research. Ten years on these spectra
will be routine, and higher resolution will be needed. I propose ``Thermal
Limit Spectroscopy'' as the next natural goal for X-ray spectroscopy. This will
open up new physics: plasma physics, velocity widths, Doppler shifts, line
profiles, and absorption lines in photoionized plasmas. A resolution of
R=3000-10,000 is required, and the technology is within reach.
