Pairing mechanisms in iron-based superconductors: variations on the s+/- theme

I will review some of the recent developments in the theory of superconductivity
of iron-based systems that go beyond the s+/- paradigm established in the early days
of the field. These include: a) prediction of and evidence for T-breaking mixed
symmetry pair states; b) influence of orbital selective correlations on pairing;
c) competition and cooperation of nematic order and superconductivity; and d) new
pair states possibly stabilized by spin-orbit coupling. A main focus will be
a critical look at the of whether Fe-pnictide based materials are fundamentally
different from Fe-chalcogenides.