  Thanks to significant improvements in high-resolution spectrographs and the
launch of dedicated space missions MOST, CoRoT and Kepler, the number of
subgiants and red-giant stars with detected oscillations has increased
significantly over the last decade. The amount of detail that can now be
resolved in the oscillation patterns does allow for in-depth investigations of
the internal structures of these stars. One phenomenon that plays an important
role in such studies are mixed modes. These are modes that carry information of
the inner radiative region as well as from the convective outer part of the
star allowing to probe different depths of the stars.
  Here, we describe mixed modes and highlight some recent results obtained
using mixed modes observed in subgiants and red-giant stars.
