Home Page of Environmental Scanning Electron Microscopy. The Environmental Scanning Electron Microscope (ESEM) is one of the major innovations and a fundamental advance in the field of electron microscopy. ESEM allows the examination of practically any specimen under any gaseous conditions, unlike conventional SEM, which operates in vacuum. An electron microscope requires a good vacuum for the generation and propagation of the electron beam, which in the past meant that the specimen under examination had to be placed also in vacuum. That condition limits the SEM, since either the specimens have to be modified and compromised by various treatments or the microscope's operational parameters must be constrained. The ESEM allows the examination of any specimen, wet or dry, insulating or conducting in situ and close to its natural state, while the environmental gas medium produces completely novel possibilities of operation and imaging. The implications of this technique go beyond the realms of microscopy, as the principle has applications to modern nanotechnologies and microengineering. Focused electron and ion beams in a controlled gaseous environment have much wider applications while capable of imaging. Physics, chemistry, biology, materials science and industrial technology can greatly benefit after the invention of ESEM. It is no exaggeration that ESEM represents, after many decades of conventional electron microscopy, the next biggest revolution in microscopy following the advent of SEM itself.