Dipole-dipole interaction is interaction of polar molecules. This type of interactions belongs to electrostatic interactions.

Interaction energy can have different sign, which depends on the orientation of dipoles. If the mutual orientation of two molecules is like this: the region of positive potential of one molecule coincides with the region, where the negative charge of the other one is localized, - then the energy is negative, that is, electrostatic interaction of the molecules results in their attraction. In this case the energy of the dipole-dipole interaction V=-2p1p2/R3,, where p1, p2 are dipolar moments of the first and the second molecules respectively.