This monograph is not simply a painstaking summary of the more patent generalities of the subject, but rather a deeply sympathetic entering into the mind of Ruysbroeck, and that, too, with no common insight. Jan van Ruusbroec, otherwise known as Ruysbroeck, is thought, by no few competent judges, to be the greatest of all medieval Catholic mystics. Very little had been written with regard to the life and doctrine of this great Flemish contemplative of the 14th century. Miss Underhill is doing lovers of not only Catholic mysticism, but also of mysticism in general, a great service with this monograph.