The dispersion interaction is a kind of intermolecular interaction that is present between any two particles, regardless of whether they possess permanent dipole moments.

Model approach to dispersion interactions is based on the fluctuations of the electron density distribution that result in fluctuating nonzero instantaneous dipole (or higher multipole) moments even in non-polar molecules. These moments further polarise the electron density distribution of neighbouring molecules and interact with the resulting instantaneous deformations of the charge distributions (in addition to the interactions caused by the permanent moments, if any).

The magnitude of dispersion interaction is directly connected with the polarisability of the interacting molecules. In the series of homologous molecules, total polarisability increases with the number of electrons in the molecule, most importantly those in its surface atoms. Thus, it generally increases with the size of the molecule, which is manifested, for example, in the increase of the boiling point of the noble gases with the period (having no permanent multipole moments, noble gas atoms are bound together through dispersion interactions only). Weakening of the dispersion interactions can be achieved through fluorination of the molecular surface, since the fluorine atoms are poorly polarisable; on the contrary, the presence of well-polarisable multi-electron atoms or, for example, conjugated -systems results in their strengthening.

For most molecules (except for small polar molecules such as molecules of water or hydrogen fluoride), the dispersion interaction is stronger than other van der Waals forces but still much weaker than a typical covalent bond. In some highly symmetric and valence saturated molecules, the dispersion interactions remain the only source of intermolecular forces. As indicated above, they are responsible for availability of the condensed phases in the inert gases despite the extremely poor polarisability of helium and neon.

Correct description of the dispersion interactions requires the quantum-mechanical approach. In particular, they can be conveniently treated with the use of the perturbation theory, as they result in small perturbation in the wave functions of isolated molecules. In this case, the mutual polarisation of the interacted molecules can be described in terms of electronically excited states, i.e. the ground state of an interacting system of molecules is described through the predominant contribution of the ground states and minor contributions of the excited states of isolated molecules. The very term "dispersion interaction" is due to the fact that the mechanism of the electronic polarisation and the approaches to its description are similar to those cases of polarisation in the electromagnetic field, i.e. the dispersion of light.

The potential of the dispersion interaction can be represented as a power series of inverse distance, where the major contribution is due to the lowest, sixth, power. Thus, the distance dependence of the dispersion forces is essentially similar to those of dipole-dipole and polarisation forces, they all being of much shorter range than the Coulomb interaction.