Many areas of physics research depend upon a good physical understanding of charged particle transport processes in gases, a statement which is as true now as it was in the early part of the last century, when modern physics was taking shape. Gas lasers, multi-wire drift chambers used in high energy particle detectors, muon-catalysed fusion in hydrogen and its isotopes and low-temperature plasma processing technology are just a few examples of experiments and processes in which electrons, ions or muons play a key role. The macroscopic properties of these non-equilibrium systems can best be found by averaging microscopic collision properties over a velocity distribution function, calculated from solution of Boltzmann's kinetic equation, using recently developed techniques. This is the realm of the modern kinetic theory of gases, and is the theme of this book.