  A number of recent experiments exhibit electronic anisotropy in the iron
pnictides, and there is a growing body of experimental evidence that its origin
is related to orbital ordering in Fe d_{xz} and d_{yz} orbitals. We examine
this problem in the parent compounds of the iron pnictides by a combination of
ab initio band theory calculations, phenomenological Ginzburg-Landau theory of
coupled orbital and magnetic order parameters, and a microscopic mean-field
study of the Kugel-Khomskii model. We find that orbital ordering is sufficient
to explain a number of key experimental observations, in particular a linear
correlation between the orthorhombic lattice distortion and the magnetic
ordered moment. We predict that orbital polarization should scale as a square
of magnetic moment close to T_N. Mediated by orbital polarization, the
effective spin-spin exchange interactions develop anisotropy in the ab-plane,
in accord with recent neutron scattering measurements.
