Volume one of Principles of Electron Optics: Basic Geometrical Optics, Second Edition, explores the geometrical optics needed to analyze an extremely wide range of instruments: cathode-ray tubes; the family of electron microscopes, including the fixed-beam and scanning transmission instruments, the scanning electron microscope and the emission microscope; electron spectrometers and mass spectrograph; image converters; electron interferometers and diffraction devices; electron welding machines; and electron-beam lithography devices. The book provides a self-contained, detailed, modern account of electron optics for anyone involved with particle beams of modest current density in the energy range up to a few mega-electronvolts. You will find all the basic equations with their derivations, recent ideas concerning aberration studies, extensive discussion of the numerical methods needed to calculate the properties of specific systems and guidance to the literature of all the topics covered. A continuation of these topics can be found in volume two, Principles of Electron Optics: Applied Geometrical Optics. The book is intended for postgraduate students and teachers in physics and electron optics, as well as researchers and scientists in academia and industry working in the field of electron optics, electron and ion microscopy and nanolithography.