Book excerpt: Diffractional Optics of Millimetre Waves combines those elements of diffraction theory normally associated with optics, including Gaussian beams, lenses, and mirrors, and extends them into the micro- and millimetre wavelength range. In this regime there are a number of applications in devices, such as automobile proximity sensors, satellite-TV receiving antennae, and non-destructive testing systems. Researchers working in these areas would benefit from greater understanding of the diffraction phenomena involved. A translated and updated version of the authors' book Diffraction Quasioptics, this book will present results formerly unavailable in the general literature.