  The High Energy Transmission Grating Spectrometer (HETGS) onboard the Chandra
X-ray Observatory has so far produced a large number of high resolution X-ray
spectra with unprecedented spectroscopic details. Spectra from outflows in
galactic and extragalactic X-ray sources indicate plasmas with a wide range of
properties. Optically thick fluorescent matter and warm photoionized regions
play as much a role as very hot regions where collisional ionization and
scattering dominate the emission. Through the measurements of blue- and
redshifts the complex dynamics of these plasmas is revealed. Quite intriguing
in this respect is the case of X-ray absorption of neutral matter. In many
cases spectral features are found to be of high complexity though the detection
of edges from intermediate Z elements as well as absorption lines from
monatomic species to molecular compounds. With the application of line
diagnostic tools and more accurate atomic data bases we are now able to model
the properties of these plasmas as well as measure line shifts and shapes to
constrain their spatial distribution and dynamics. In various examples, i.e.
plasmas from accretion disks, winds, stationary clouds as well as the ISM, the
power of highly resolved X-ray spectra is demonstrated and the scientific
capability of XEUS in this context is explored.
