Intermolecular interaction has an electrostatic nature. The assumption of its existence was first postulated by J.D. Van der Waals (1873) in order to explain the properties of real gases and liquids. In its broadest sense, this term can refer to such interaction between any particles (molecules, atoms, ions) that does not result in formation of chemical, i.e. ionic, covalent or metallic bonds. In other words, these interactions are much weaker than covalent bonds and do not lead to a substantial reorganisation of electronic structure of the interacting particles.

At large distances the attractive forces predominate; they can have an orientation, polarisation (induction) or dispersion character (for details, see the articles on van der Waals interaction and dispersion interactions). When averaged over the particle rotation that occurs as a result of thermal motion, the potential of intermolecular forces is inversely proportional to the sixth power of the distance, and the potential of ion-dipole forces (with permanent or induced dipoles) – to the fourth power. At small distances, the repulsive forces between the electron shells of the particles dominate. A special case is manifested by hydrogen bonds – attractive interactions between a hydrogen atom of one molecule and an electronegative atom of another molecule that occur at shorter distances when the atoms carry sufficiently large effective charges.

The packing of particles and the distance between them in the condensed phase, as determined by the equilibrium between attraction and repulsion, can be predicted from the van der Waals radii of the constituent atoms of the molecule (ion radii in the case of ions): the distance between the atoms of different molecules must not exceed the sum of the radii of these atoms. The molecular interactions are modeled using empirical potentials, including the best-known Lennard-Jones potential (repulsion is described by the twelfth power of the inverse distance, attraction by the sixth power) and Buckingham potential (with a more physically justified exponential repulsion), the first being more convenient for the calculations. In the condensed phase, where the multipole expansion cannot be applied to the molecules due to the proximity of the molecules to each other, the method of atom-atom potentials can be applied; it is based on the same potentials, but applied to pairwise interactions of atoms and augmented with Coulomb terms describing the interaction of their effective charges.