  High temperature superconductivity in iron pnictides and chalcogenides
emerges when a magnetic phase is suppressed. The multi-orbital character and
the strength of correlations underlie this complex phenomenology, involving
magnetic softness and anisotropies, with Hund's coupling playing an important
role. We review here the different theoretical approaches used to describe the
magnetic interactions in these systems. We show that taking into account the
orbital degree of freedom allows us to unify in a single phase diagram the main
mechanisms proposed to explain the (\pi,0) order in iron pnictides: the
nesting-driven, the exchange between localized spins, and the Hund induced
magnetic state with orbital differentiation. Comparison of theoretical
estimates and experimental results helps locate the Fe superconductors in the
phase diagram. In addition, orbital physics is crucial to address the magnetic
softness, the doping dependent properties, and the anisotropies.
