  The recently discovered Fe-pnictide and chalcogenide superconductors display
low-temperature properties suggesting superconducting gap structures which
appear to vary substantially from family to family, and even within families as
a function of doping or pressure. We propose that this apparent nonuniversality
can actually be understood by considering the predictions of spin fluctuation
theory and accounting for the peculiar electronic structure of these systems,
coupled with the likely 'sign-changing s-wave' (s\pm) symmetry. We review
theoretical aspects, materials properties and experimental evidence relevant to
this suggestion, and discuss which further measurements would be useful to
settle these issues.
