The orange system of FeO has been reinvestigated using low-temperature molecular beam laser-induced fluorescence spectra, obtained by supersonic jet cooling. Two new weak bands have been found, and analyses of some of the previously known bands extended. Measurements of the 54Fe-56Fe isotope shifts have been made for most of the bands, and the hyperfine structure of the low-J lines has been recorded for two of the strongest bands of 57FeO. The isotope shifts are consistent with the presence of two 5Δi-5Δi transitions lying within 1000 cm-1; the origins of the Ω = 4 spin components lie at 5583 and 6110 Å, respectively. The hyperfine patterns and the spin-orbit structure indicate that the upper state electron configurations are (3dδ)3 (3dπ)2 (3dσ)1, (D5Δi, 5583 Å) and O(2pπ)3 (4sσ)1 (3dδ)3(3dπ)3, (D′5Δi, 6110 Å). The bond length in the D′ state (r0 = 1.654 Å) has been obtained from a deperturbation of the 6110 Å band; it is only 0.035 Å longer than in the ground state, which indicates that electron promotion between the two π orbitals, nominally O(2pπ) and Fe(3dπ), has only a small effect on the strength of the bonding. The new isotope data still do not clarify the vibrational assignments of the higher levels, which are disorganized by extensive electronic perturbations.