When Dr. Romana Guarnieri, in a letter to Osservatore Romano (16 June 1946), announced her discovery that Margaret Porette (d. 1 June 1310) was the author of The Mirror of Simple Souls, certainly a major French document of pre-Reformation spirituality, a sensation was created in the academic world. Although The Mirror is one of the few heretical documents to have survived the Middle Ages in its entirety, both its title and its authorship were among the most persistent and troublesome problems of scholarly research in the field of medieval vernacular languages. The Mirror, in its original French, survives only in the fifteenth-century manuscript which the great Condé (Louis II de Bourbon) had acquired for his palace at Chantilly. And, so far as can be known, all that remains with which to compare the readings of this manuscript text are those translations of The Mirror which, also in manuscript, are to be found in Latin, Italian, and Middle English. This edition of The Mirror of Simple Souls is a translation from the French original with interpretive essays by Edmund Colledge, O.S.A., Judith Grant, and J.C. Marler, and a foreword by Kent Emery, Jr. The translators of this Modern English version rely primarily on the French, yet take other medieval translations into account. As a result, this edition offers a reading of The Mirror which solves a number of difficulties found in the French, and the introductions contributed by the translators narrate the archival history of the book, for which Margaret Porette was burned alive in Paris in 1310.