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.