  The present article reviews recent experimental investigations of spin
dynamics in iron-based superconductors and their parent compounds by means of
inelastic neutron scattering. It mainly focuses on the most contemporary
developments in this field, pertaining to the observations of magnetic resonant
modes in new superconductors, spin anisotropy of low-energy magnetic
fluctuations that has now been observed in a wide range of chemical
compositions and doping levels, as well as their momentum-space anisotropy
incurred by the spin-nematic order. The implications of these new findings for
our understanding of the superconducting state, along with the remaining
unsettled challenges for neutron spectroscopy, are discussed.
