  The evolution and escape of the martian atmosphere and the planet's water
inventory can be separated into an early and late evolutionary epoch. The first
epoch started from the planet's origin and lasted $\sim$500 Myr. Because of the
high EUV flux of the young Sun and Mars' low gravity it was accompanied by
hydrodynamic blow-off of hydrogen and strong thermal escape rates of dragged
heavier species such as O and C atoms. After the main part of the
protoatmosphere was lost, impact-related volatiles and mantle outgassing may
have resulted in accumulation of a secondary CO$_2$ atmosphere of a few tens to
a few hundred mbar around $\sim$4--4.3 Gyr ago. The evolution of the
atmospheric surface pressure and water inventory of such a secondary atmosphere
during the second epoch which lasted from the end of the Noachian until today
was most likely determined by a complex interplay of various nonthermal
atmospheric escape processes, impacts, carbonate precipitation, and
serpentinization during the Hesperian and Amazonian epochs which led to the
present day surface pressure.
