Field Electron Emission from Metals -- Characteristics of Field Emission at Very High Current Densities -- Maximum Field Emission Current Densities -- Field Emission In Microwave Field -- Field Emission from Semiconductors -- Statistics of Field Electron Emission -- The Use of Field Emission Cathodes in Electron Optical Systems: Emission Localization to Small Solid Angles -- Advances in Applications.Field emission is a phenomenon described by quantum mechanics. Its emission capability is millions times higher than that of any other known types of electron emission. Nowadays this phenomenon is experiencing a new life due to wonderful applications in the atomic resolution microscopy, in electronic holography, and in the vacuum micro- and nanoelectronics in general. The main field emission properties, and some most remarkable experimental facts and applications, are described in this book.