  The evolution of the N=28 shell closure is investigated far from stability.
Using the latest results obtained from various experimental techniques, we
discuss the main properties of the N=28 isotones, as well as those of the N=27
and N=29 isotones. Experimental results are confronted to various theoretical
predictions. These studies pinpoint the effects of several terms of the
nucleon-nucleon interaction, such as the central, the spin-orbit, the tensor
and the three-body force components, to account for the modification of the
N=28 shell gap and spin-orbit splittings. Analogies between the evolution of
the N=28 shell closure and other magic numbers originating from the spin-orbit
interaction are proposed (N=14,50, 82 and 90). More generally, questions
related to the evolution of nuclear forces towards the drip-line, in bubble
nuclei, and for nuclei involved in the r-process nucleosynthesis are proposed
and discussed.
