The binding energies, structural parameters, and vibrational frequencies of FeCO, FeCO-, and FeCO+ were studied with a Linear combination of Gaussian-type orbitals-density functional (LCGTO-DF) method. The ground state of FeCO is found to be (3) Sigma(-) and the calculated dissociation energy, with respect to ground state Fe(D-5,3d(6)4s(2)) and CO ((1) Sigma(+)), is 30 kcal/mol; after correcting for the atomic states separation of the iron atom this value becomes 17 kcal/mol, which is relatively close to the most recent experimental values 8.1+/-3.5-10.5+/-3.7 kcal/mol. Quartet ground states were found for both FeCO+ and FeCO- and the calculated dissociation energies (with respect to ground state Fe+ Fe-, and CO) are 50 and 31 kcal/mol, respectively. There is agreement between theory and experiment in that D(FeCO+)>D(FeCO-)>D(FeCO). The omega(e)’s we calculate for FeCO are, in cm(-1) 658 (Fe-C stretch), 1982 (C-O stretch), and 368 (bend). These values are reasonably close to their experimental counterparts, 530+/-10, 1950+/-10, and 330+/-50. For FeCO- we have found 566 and 272 cm(-1) for the Fe-C stretch and bend modes while the experimental values are 465+/-10 and 230+/-40 cm(-1). A frequency of 1831 cm(-1) is predicted for the C-O stretch of FeCO-. The sigma-donation (CO-->Fe) and pi-back-donation (Fe-->CO) charge transfer mechanism is operative in these species.