In the first decade of the 20th century, nearly a hundred years of work on thephenomenon of Brownian motion culminated in theory and experiments thatdemonstrated irrefutably the discontinuous or molecular nature of matter.Colloidal suspensions and the phenomenon of Brownian motion thus became thekey to confirmation of the ‘new world-view’ of statistical mechanics, the statisticalbasis of thermodynamics. One may conveniently identify four ‘stages’ in thehistorical development of ‘Brownian motion science’, characterized in turn bydiscovery, observation, theoretical prediction, and quantitative confirmation. Weare living, of course, in the fifth stage, that of application: the modern disciplineof ‘soft matter’.