A SIMPLIFIED VERSION. The "Interior Castle" or "Book of Mansions", contains the essence of St. Teresa of Avila's doctrine on prayer. Presented in a simpler form than the original, the text of this book remains faithful to St. Teresa's thought, wording and expression. The continuity of thought is retained - this book is not a series of quotations. It is hoped that it will provide an easy introduction to the reading of the full text of the "Interior Castle". This book also serves as a companion to "The Way of Perfection" by the same author.