J.D. van der Waals, noble prize for chemistry in 1910.

Fluctuations of electrons are responsible for the existence of short-term partial charges in the electronic sheaths of atoms and molecules. Atoms or molecules in close vicinity influence each other in such a way that the partial charges become opposed to each other. This crosstalk of charges leads to an attraction of the atoms/molecules in question.

Van der Waals bonds are weak and are only effective over short distances. Nevertheless, they are important for the aggregation of molecules and for the folding of macromolecules.