Writers have more than once pointed out that the ‘Ancren Riwle’ is far from being a mere set of austere regulations for a unique and now obsolete type of contemplative life. They have shown that during the later middle ages this Rule was regarded in England as a spiritual classic for every type of Christian, for it is in fact, chiefly concerned with the principles of a good Christian life which it sets forth with great charm and ability. But it is perhaps not so often realized that this fact follows from the very definite conception of the meaning and value of any rule, which the author outlines in his Prologue. All those who are resolved to fulfil their lives as good Christians should study this concise and attractive treatment of the meaning of rule in a good life. The ‘Ancren Riwle’ was written half a century before St. Thomas wrote his Summa Theologica, but the fundamental truths of this Prologue are endorsed by him. Thus those three sisters for whom the Riwle was written, and all those of every station in life who have since read it, have been inspired by truly Thomistic principles. It may, therefore, be of value to set forth the ideas contained in the Prologue of this Rule of Anchoresses.