The environmental scanning electron microscope (ESEM) is a scanning electron microscope (SEM) that allows for the option of collecting electron micrographs of specimens that are wet, uncoated, or both by allowing for a gaseous environment in the specimen chamber. Although there were earlier successes at viewing wet specimens in internal chambers in modified SEMs, the ESEM with its specialized electron detectors (rather than the standard Everhart-Thornley detector) and its differential pumping systems, to allow for the transfer of the electron beam from the high vacuum in the gun area to the high pressure attainable in its specimen chamber, make it a complete and unique instrument designed for the purpose of imaging specimens in their natural state. The instrument was designed originally by Gerasimos Danilatos while working at the University of New South Wales. History Starting with Manfred von Ardenne, early attempts were reported of the examination of specimens inside "environmental" cells with water or atmospheric gas, in conjunction with conventional and scanning transmission types of electron microscopes. However, the first images of wet specimens in an SEM were reported by Lane in 1970 when he injected a fine jet of water vapor over the point of observation at the specimen surface; the gas diffused away into the vacuum of the specimen chamber without any modification to the instrument. Further, Shah and Beckett reported the use of differentially pumped cells or chambers to presumably maintain botanical specimens conductive in order to allow the use of the absorbed specimen current mode for signal detection in 1977 and in 1979. Spivak et al. reported the design and use of various environmental cell detection configurations in an SEM including differential pumping, or the use of electron transparent films to maintain the specimens in their wet state in 1977. Those cells, by their nature, had only limited application use and no further development was done. In 1974, an improved approach was reported by Robinson with the use of a backscattered electron detector and differential vacuum pumping with a single aperture and the introduction of water vapor around 600 Pa pressure at the freezing point of temperature. However, neither of those approaches produced a stable enough instrument for routine operation. Starting work with Robinson in 1978 at the University of New South Wales in Sydney, Danilatos undertook a thorough quantitative study and experimentation that resulted in a stable operation of the microscope at room temperature and