  In this review, we describe the experimental facilities and methods which
make it possible to produce and measure the properties of the extreme neutron
rich nuclei. We then develop the theoretical framework that will accompany us
along the review; the shell-model approach with large scale configuration
interaction (mixing) SM-CI, with special emphasis in the competition between
the spherical mean field and the nuclear correlations (mainly pairing and
quadrupole-quadrupole). The symmetry properties of the latter are treated in
detail as they will show to be of great heuristic value. We explore in detail
the Islands of Inversion (IoI) at N=20 and N=28. We make a side excursion into
the heavier Calcium and Potassium isotopes, to discuss current issues on shell
evolution and new magic numbers far from stability. We visit the N=40 Island of
Inversion. We discuss the doubly magic nucleus 78Ni, its shape coexistence and
the prospect of a new IoI at N=50 below Z=28. We examine the N=70 and N=82
neutron closures approaching the neutron drip line.
