London dispersion forces are the weakest component of Van der Waals interactions. They arise from attractions between instantaneously induced dipoles on neighbouring atoms. Their relative weakness, in particular for light atoms, such as hydrogen, has led to their importance being largely ignored in discussions of molecular stability and reactivity. This Review highlights the influence of these attractive forces — usually between C–H moieties in ancillary ligands — on the physical and chemical properties of organometallic and inorganic molecules. We feature recent examples of organic species that have informed current thinking and follow with a discussion of several prominent inorganic and organometallic complexes wherein dispersion forces have been explicitly identified or calculated. These forces strongly influence the behaviour of such complexes and often have a defining structural role. Attention is also drawn to several compounds in which significant attractive dispersion forces are probably present but have not been investigated.Despite its relative weakness, the London dispersion force can strongly influence physical and chemical properties of molecules. This Review highlights how structure and reactivity of organometallic and inorganic molecules are greatly affected by the cumulative effect of this force.