In 1818, Mother Rose Philippine Duchesne, of the newly-founded Society of the Sacred Heart of Jesus, left France to participate in the missionary expansion of the Catholic Church in the New World, at the request of Bishop Louis William Dubourg, named bishop of Louisiana. This vast area, acquired by the United States from France in 1803, extended over a territory of 530,000,000 acres (828,000 square miles), from New Orleans to Canada, including all the lands drained by the vast river system of the Mississippi and the Missouri, the future Midwest of the Unites States. Navigation was often difficult and the postal system disrupted. The writings of Saint Philippine-656 letters, five journals and a few shorter documents, all in French (except for one letter in English)-constitute a rich source of information about her missionary call and the sacrifices involved, the primitive life of the first years on the Missouri frontier, and the development of the Catholic Church and the Society of the Sacred Heart in North America during thirty-four years. They depict her heroic life, widely recognized by historians of pioneer American Catholic life, and reveal her holiness, proclaimed by the Catholic Church in 1988. All of her writings have not been available to readers and researchers until now. This annotated edition brings them all together.