High-voltage electron microscopy has a number of very obvious advantages in the study of thin crystals, particularly where thicker samples can be observed at greatly increased contrast than at standard voltages of 100 kV. High-voltage electron microscopes - those operating at accelerating potentials of 200 kV and above were developed concurrently with the more conventional electron microscopes in the years just before World War II. While a treatment of design features is not necessarily germane to people's understanding of the applications of high-voltage electron microscopy, there are several features that, on clarification, may enhance a person's appreciation of the high-voltage electron microscope. Enlargement of the lenses sometimes necessitates the enlargement of the pole pieces, with the result that the spherical aberration coefficients for the lenses increase. The really unique feature of the high-voltage microscope design is the high-voltage power source; not necessarily because of its circuit design, but because of its overall engineering.