  The nuclear shell model is a benchmark for the description of the structure
of atomic nuclei. The magic numbers associated with closed shells have long
been assumed to be valid across the whole nuclear chart. Investigations in
recent years of nuclei far away from nuclear stability at facilities for
radioactive ion beams have revealed that the magic numbers may change locally
in those exotic nuclei leading to the disappearance of classic shell gaps and
the appearance of new magic numbers. These changes in shell structure also have
important implications for the synthesis of heavy elements in stars and stellar
explosions. In this review a brief overview of the basics of the nuclear shell
model will be given together with a summary of recent theoretical and
experimental activities investigating these changes in the nuclear shell
structure.
