  Chandra has significantly advanced our knowledge of the processes in the
intracluster gas. The discovery of remarkably regular ``cold fronts'', or
contact discontinuities, in merging clusters showed that gas dynamic
instabilities at the boundaries between the moving gases are often suppressed,
most likely by specially structured magnetic fields.
  Cold fronts are not limited to mergers -- Chandra observed them in the cores
of more than 2/3 of the cooling flow clusters, where they often divide the cool
central and the hotter ambient gas phases. The natural state of the low-entropy
central gas in clusters thus appears to be to slosh subsonically in the central
potential well, with several interesting implications. Hydrostatic equilibrium
is not reached and the hydrostatic total mass estimates cannot be valid at
small radii (r<100 kpc). The kinetic energy dissipated by the sloshing gas may
be sufficient to compensate for radiative cooling. In the absence of a recent
merger, the cause of such sloshing is unclear. It might be related to the
mechanical energy generated by the central AGN, evidence of which (the bubbles)
is also observed by Chandra in a large fraction of the cooling flow clusters.
  Heat conduction across cold fronts is suppressed completely. In the bulk of
the gas, it is reduced by a factor of ~10 or more relative to the classic
value, as shown by merger temperature maps. A spatial correlation between the
gas temperature maps and the radio halo maps is observed in several mergers,
which may provide clues for the relativistic particle acceleration mechanisms.
