The aim of this book is merely to set forth a few of the more widely approved methods of mental prayer. Strong in the strength of its own objectivity, this book is offered to all souls desirous of making acquaintance with an art so lofty and so profitable as that of how to pray. That is why this book is addressed in a special way to priests and clerics. So, it is appropriate that the spiritual director should be conversant with the various methods of prayer which the different currents of spirituality have at various times been brought into use, and which have by won now for themselves an assured place in Christian asceticism. But this book is also addressed in a special way to another class of souls. This book is meant to help those who, especially in novitiates, are charged with the duty of the religious training of souls who have this vocation, by putting them in touch with the great traditional schools of prayer.