  The Kepler mission observed many thousands of red giants. The long time
series, some as long as the mission itself, have allowed us to study red giants
with unprecedented detail. Given that red giants are intrinsically luminous,
and hence can be observed from very large distances, knowing the properties of
red giants, in particular ages, is of immense value for studies of the
formation and evolution of the Galaxy, an endeavor known as "Galactic
archaeology". In this article we review what we have learned about red giants
using asteroseismic data. We start with the properties of the power spectrum
and move on to internal structure and dynamics of these stars; we also touch
upon unsolved issues in red-giant asteroseismology and the prospects of making
further progress in understanding these stars.
