The interference energy partitioning analysis method developed by our group and used to study the nature of the chemical bond was extended to partition the electric dipole moment in quasi-classical and interference contributions. Our results show that interference participates in charge displacement in polar molecules, providing, directly or indirectly, a relevant contribution for the total dipole moment. A linear correlation was found between the interference contribution of the dipole moment from the bond electron group, mu(INT)(bond), and the difference of electronegativity of the atoms which form the bond, Delta X-AB. This interesting result reinforces the fact that electronegativity is not a property of an atom alone, but rather a property of the atom in the molecule and that Delta X-AB can only be associated with that part of the total charge displacement resulting from the formation of the chemical bond. The partitioning of the total dipole moment into quasi-classical and interference contributions provides new insights about the reasons for the failure of the Delta X-AB criterion in predicting the correct orientation of the dipole moment in several molecules. The results of the present work also bring additional evidence for the previously proposed mechanism of formation of polar bonds.