Although Catherine of Siena was proclaimed a Doctor of the Church in 1970, relatively little attention has been given to her mystical thought, particularly in the English-speaking world. The Dialogue, the famous compendium of her mature thought, is difficult to understand owing to its interruptions, repetitions, overlapping arguments, imagery and undefined terms. Thomas McDermott breaks new ground in his systematic presentation of Catherine's teachings. Drawing on the Dialogue and also on Catherine's 381 letters and prayers, he explains clearly her principal teachings in relation to spiritual development, and identifies Catherine's possible sources as well as her areas of originality. By examining Catherine's life and mystical experiences, McDermott shows how she herself grew spiritually and how her growth corresponds to her later teaching on the "three stairs" on the "bridge of Christ crucified." Finally, the author puts forward what he regards as the fundamental message of Catherine's life and teaching. Students of mysticism and spirituality will find this book a trustworthy guide through the incredibly rich mysticism of one of the 14th century's most amazing women.