This book provides an elementary, complete account of quasi-Frobenius rings at a level allowing researchers and graduate students to gain entry to the field. A ring is called quasi-Frobenius if it is "right" or "left" selfinjective, and "right" or "left" artinian (all four combinations are equivalent). The study of these rings grew out of the theory of representations of a finite group as a group of matrices over a field, and the present extent of the theory is wide-ranging.