  We propose orbital fluctuations in a multi-band ground state as the
superconducting pairing mechanism in the new iron-based materials. We develop a
general SU(4) theoretical framework for studying a two-orbital model and
discuss a number of scenarios that may be operational within this orbital
fluctuation paradigm. The orbital and spin symmetry of the superconducting
order parameter is argued to be highly non-universal and dependent on the
details of the underlying band structure. We introduce a minimal two-orbital
model for the Fe-pnictides characterized by non-degenerate orbitals that
strongly mix with each other. They correspond to the iron "d_xy" orbital and to
an effective combination of "d_zx" and "d_zy", respectively. Using this
effective model we perform RPA calculations of susceptibilities and effective
pairing interactions. We find that spin and orbital fluctuations are,
generally, strongly coupled and we identify the parameters that control this
coupling as well as the relative strength of various channels.
