The development of molecular physics and physical chemistry cannot be understood without a knowledge of the work of the Dutch physicist Johannes Diderik van der Waals. His doctoral thesis of 1873 was the first theory of liquids and gases in which the essential differences and similarities of these two phases were interpreted in terms of the properties of the constituent molecules.

For forty years he and his school held fast to the view that atoms, molecules, and their interactions were the basis of much physics and chemistry and, by example rather than direct attack, rebutted the anti-atomistic views of Mach, Ostwald, Duhem, and the other 'energeticists'. The Dutch contribution to physical science had never been greater, nor has it ever again had the influence that it manifested in the forty years before the outbreak of the First World War in 1914.

Van der Waals was the senior member of the group of physicists responsible for this surge, and his life and work are an essential component of any attempt to understand the scientific history of this period.