William Farr: founder of modern concepts of surveillance.

Considerable confusion surrounds the use of the term surveillance in the context of public health but the principles underlying all uses are as old as epidemiology itself. William Farr has contributed more than anyone else to the development of these principles and to the demonstration of their value in practice on a large scale. This paper re-examines the basic tenets which guided him and the methods and techniques which he developed in the hope of reviving insights and resetting standards that modern epidemiologists might, with benefit, strive to emulate.