  Superconductivity in the iron pnictides and chalcogenides is closely
connected to a bad-metal normal state and a nearby antiferromagnetic order.
Therefore, considerable attention has been focused on the role of electron
correlations and spin dynamics. In this article, we summarize some key
experiments that quite directly imply strong electron correlations in these
materials, and discuss aspects of the recent theoretical studies on these
issues. In particular, we outline a $w$-expansion, which treats the correlation
effects using the Mott transition as the reference point. For the parent
systems, it gives rise to an effective J1-J2 model that is coupled to the
itinerant electrons in the vicinity of the Fermi energy; this model yields an
isoelectronically-tuned quantum critical point, and allows a study of the
distribution of the spin spectral weight in the energy and momentum space in
the paramagnetic phase. Within the same framework, we demonstrate the Mott
insulating phase in the iron oxychalcogenides as well as the alkaline iron
selenides; for the latter system, we also consider the role of an
orbital-selective Mott phase. Finally, we discuss the singlet superconducting
pairing driven by the short-range J1-J2 interactions. Our considerations
highlight the iron pnictides and chalcogenides as exemplifying
strongly-correlated electron systems at the boundary of electronic localization
and itinerancy.
