Abstract: | Recent progress in studies of globular clusters has shown that they are not simple stellar populations, but rather are made
up of multiple generations. Evidence stems both from photometry and spectroscopy. A new paradigm is arising for the formation
of massive star clusters, which includes several episodes of star formation. While this provides an explanation for several
features of globular clusters, including the second-parameter problem, it also opens new perspectives on the relation between
globular clusters and the halo of our Galaxy, and by extension on all populations with a high specific frequency of globular
clusters, such as, e.g., giant elliptical galaxies. We review progress in this area, focussing on the most recent studies.
Several points remain to become properly understood, in particular those concerning the nature of the polluters producing
the abundance pattern in the clusters and the typical timescale, the range of cluster masses where this phenomenon is active,
and the relation between globular clusters and other satellites of our Galaxy. |