Considerable attention has been focussed on non-aqueous chemistry in the last decade and this situation has arisen no doubt from a realization of the vast application of this branch of chemistry. Within this field much energetic work has been channelled into the determination of the coordination chemistry of tran­ sition metals in these solvent 8ystems. Elaborate experimental techniques have been developed to discover, in particular, the magnetic and spectral properties of complex compounds, and the theoretical background of such systems has been expanded to corroborate, as far as possible, the experimental results. This text has, however, a different bias from many books currently available on this branch of chemistry, and is designed to be a survey of known facts on many of the non-aqueous solvents currently in use mainly in the field of halogen chemistry, together with a discussion of these facts in the light of accepted principles. As such, it is hoped to close a gap in the literature of which many workers and advanced students in this field will be aware. The treatment is meant to be selective rather than completely comprehensive and must unevitably reflect some of the special interests of the author.