Among all the writings of St. Teresa of Avila, the Interior Castle is the work which is most appropriate for the study of the ascetical and mystical life. Chronologically it is her last book and it shows the saint's spiritual maturity. She takes up the rich treasury of experiences which she relates in the book of her Life, the Way of Perfection and also in the Spiritual Testimonies (or the Favors Received from God) and she presents these in a less personal and descriptive form. By following her counsels in this book, Fr. Otger Steggink opens up for us the path of contemplation as understood in the Carmelite school. Fr. Steggink was one of the world's foremost authorities on the spirituality of St. Teresa of Avila.