A linear correlation between the bond orders and stretching force constants of bonds, which appears to have general application, is derived on the basis of a potential energy function previously used by Pauling in a correlation of C—C bond length with bond order. The relationship is shown to be consistent with predicted bond orders and experimentally determined force constants of C—C, C—O, N—N, and N—O bonds.The possible effects of anharmonicity and resonance energy on the force constant and equilibrium C—C bond distance are considered for the case of the benzene molecule, and it is concluded that the best agreement with experiment is obtained if we postulate a low degree of anharmonicity and allow for the change of resonance energy with bond distance.