The LCAO‐MO SCF orbitals for the 1Σ+ ground state of carbon monoxide, constructed from 1s, 2s, and 2p atomic functions, have been calculated for 11 internuclear distances between 1.5 and 4.0 a.u. Using the unoccupied SCF orbitals a number of lower excited states have been calculated. The equilibrium distances, force constants, and ν00 energies have been calculated from the curves of E vs R for these various states. As these calculated curves do not separate at infinity into the atoms in their proper spectroscopic states, configuration interaction has been carried out with functions which cross the computed curves and separate into the atoms in their 3P states. The lower states of carbon monoxide seem to be divided into three classes: (a) those which are reasonably well represented by our functions, namely, X 1Σ+, e 3Σ—, a′ 3Σ+, A 1Π, and a 3Π; (b) those which are not at all well represented by our functions, namely, b 3Σ+, B 1Σ+, and C 1Σ+; (c) those states for which the experimental assignment may be in error, namely, d 3Π and F 1Π.