Volume III/27 covers the magnetic properties of inorganic compounds based on transition elements. It can therefore be considered as a supplement to volumes III/4 and III/12 compounds which appeared in 1970 and in the period 1978 - 1982 respectively. In a way this volume also forms a counterpart to volume III/19, in which the magnetic properties of metals, alloys and metallic compounds are compiled. The present subvolume III/27h on oxides covers those crystalline and vitreous oxidic boron compounds for which the magnetic properties primarily depend on the presence of 3d transition elements in the structure. Much attention is given to the relation between the optical and the magnetic properties of the various substances.