  High-spectral resolution observations of clusters of galaxies are a powerful
tool to understand the physical processes taking place in these massive
objects. Their hot multi-million-degree X-ray emitting cluster atmospheres,
containing most of the baryons in these systems, are enriched to around 1/3 of
the solar metallicity. Therefore, cluster spectra host a variety of spectral
lines, in particular, the Fe-L complex around 1 keV typically emitted from
cooler systems and Fe-K at 6.7 keV seen from more massive clusters. The line
ratios and continuum are sensitive probes of the temperature distribution of
the gas, while the strength of lines compared to the continuum measures
metallicity. With sufficient spectral resolution, the velocity structure can be
obtained from line widths and shifts in position. Using detailed modelling, we
can then understand better processes such as feedback from active galactic
nuclei, mergers and enrichment, that are taking place in clusters.
