Detailed transmission electron microscopy (TEM), x-ray diffraction (XRD), and optical characterization of a variety of InN thin films grown by molecular beam epitaxy under both optimized and non-optimized conditions is reported. Optical characterization by absorption and photoluminescence confirms that the band gap of single crystalline and polycrystalline wurtzite InN is 0.70 {+-} 0.05 eV. Films grown under optimized conditions with a AlN nucleation layer and a GaN buffer layer are stoichiometric, single crystalline wurtzite structure with dislocation densities not exceeding mid-10{sup 10} cm{sup -2}. Non-optimal films can be poly-crystalline and display an XRD diffraction feature at 2{theta} {approx} 33{sup o}; this feature has been attributed by others to the presence of metallic In clusters. Careful indexing of wide angle XRD scans and selected area diffraction patterns shows that this peak is in fact due to the presence of polycrystalline InN grains; no evidence of metallic In clusters was found in any of the studied samples.