Abstract
The Third International Summer Institute in Surface Science is dedicated to the memory of Erwin W. Muller. It is, therefore, most appropriate to include a discussion of field emission microscopy, which he founded with his invention of the field emission microscope (FEM) in 1937. Although most of Müller's efforts in the last 20 years were devoted to field ion microscopy and related subjects, his pioneering efforts set the stage for much of the work done in both field emission and field ion microscopy.