The development of molecular physics and physical chemistry cannot be understood without a knowledge of the work of 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. This view contradicted the work of Mach, Ostwald, Duhem and other "energeticists" and provides the foundation for our current understanding of fluids. In the years since the end of World War II, there has been a re-appraisal of van der Waals's work, which has established his historic place as one of the founders of molecular science. This is the only biography of Johannes van der Waals and should be read by anyone with an interest in the history of physics and chemistry, and its most important innovator.