  The electronic states and superconductivity in iron pnictides are studied on
the basis of the 16 band $d$-$p$ model which includes both the onsite Coulomb
interaction between Fe $d$ electrons and the intersite one between Fe $d$ and
pnictogen $p$ electrons. The model well accounts for experimentally observed
two fluctuations: the $d$-$d$ interaction-enhanced antiferromagnetic (AFM)
fluctuation and the $d$-$p$ interaction-enhanced ferro-orbital (FO) fluctuation
responsible for the $C_{66}$ elastic softening. The AFM fluctuation induces the
repulsive pairing interaction for $\bm{q}\sim \bm{Q}_{\rm AF}$ while the FO
does the attractive one for $\bm{q}\sim \bm{0}$ resulting in the $s_{\pm}$-wave
superconductivity where the two fluctuations cooperatively enhance the
superconducting transition temperature $T_{c}$ without any competition by
virtue of the $\bm{q}$-space segregation.
