  In this paper we review the properties of the 1/$N_f$ expansion in
multidimensional theories. Contrary to the usual perturbative expansion it is
renormalizable and contains only logarithmic divergencies. The price for it is
the presence of ghost states which, however, in certain cases do not contribute
to physical amplitudes. In this case the theory is unitary and one can
calculate the cross-sections. As an example we consider the differential cross
section of elastic $eq \to eq$ scattering in $D=7,11,...$-dimensional world. We
look also for the unification of the gauge couplings in multidimensional
Standard Model and its SUSY extension which takes place at energies lower than
in 4 dimensions.
