The book contains authoritative review articles by the world's leading experts on non-equilibrium processes in gases which are pertinent to the study of the forces between molecules. The reviews therefore encompass both theoretical and experimental studies of the bulk properties of gases, such as the viscosity and thermal conductivity and ion mobility, with particular reference to the effects of electric and magnetic fields. The text also contains a summary of the current state of the theoretical treatment of the forces between molecules, together with the experimental study of these forces by means of molecular beam scattering and various kinds of molecular spectroscopy. The molecular systems discussed are all polyatomic and there is particular emphasis on the anisotropy of the intermolecular potential and its effects. The volume is unique in that it brings together a number of strands of current attempts to elucidate the forces between molecular systems.