As happens in other scientific and technological systems, cavitation has been responsible for the innovation of numerous specialised experimental methods. While progress in the study of some aspects of cavitation was made, thanks to the employment of methods already in use in other domains, the study of certain other aspects necessitated the invention of original instruments and techniques. A good picture is more valuable than a long discourse. Optics has always constituted the basic technique in the study of cavitation. The phenomenon of cavitation can easily be visualised, at least in cold water, given the large discontinuity of the refractive index at the air-liquid interfaces. No test of cavitation is considered good unless a stroboscope is used in carrying it out; a stroboscope is the basic source of illumination which makes it possible to visualise rapid phenomena.