  We present an overview of observational progress in the study of
extragalactic globular cluster systems. Globular clusters turn out to be
excellent tracers not only for the star-formation histories in galaxies, but
also for kinematics at large galactocentric radii. Their properties can be used
to efficiently constrain galaxy formation and evolution. After a brief
introduction of the current methods and futures perspectives, we summarize the
knowledge gained in various areas of galaxy research through the study of
globular clusters. In particular, we address the star-formation histories of
early-type galaxies; globular cluster population in late-type galaxies and
their link to early-type galaxies; star and cluster formation during mergers
and violent interactions; and the kinematics at large radii in early-type
galaxies. The different points are reviewed within the context of galaxy
formation and evolution.
  Finally, we revisit the globular cluster luminosity function as a distance
indicator. Despite its low popularity in the literature, we demonstrate that it
ranks among one of the most precise distance indicators to early-type galaxies,
provided that it is applied properly.
