  Observations of damped Lyman alpha systems offer a unique window on the
neutral-gas reservoirs that gave rise to galaxies at high redshifts. This
review focuses on critical properties such as the H I and metal content of the
gas and on independent evidence for star formation. Together, these provide an
emerging picture of gravitationally bound objects in which accretion of gas
from the IGM replenishes gas consumed by star formation. Other properties such
as dust content, molecular content, ionized-gas content, gas kinematics, and
galaxy identifications are also reviewed. These properties point to a
multiphase ISM in which radiative and hydrodynamic feedback processes are
present. Numerical simulations and other types of models used to describe
damped Lyman alpha systems within the context of galaxy formation are also
discussed.
