Catherine of Siena (b. 1347–d. 1380) was an author, spiritual leader, religious reformer, and one of the more remarkable public figures of the Middle Ages. Born to a prosperous family of cloth dyers, in her youth she developed a reputation for unusual piety, and in her late teens or early twenties joined the local community of Dominican female penitents (precursors to what became in the 15th century the Dominican Third Order). She developed a following that included a number of young Sienese nobleman, as well as religious from various orders, and in 1374 was enlisted by the Dominican order and the papacy to help advance several causes, including a Crusade to the Holy Land and peace in Italy. Between 1374 and her death in 1380, through her letters and in person, Catherine advocated for ecclesiastical reform, the return of the papacy to Rome from Avignon, and the Roman observance after the schism of 1378. In addition to her letters—the largest epistolary collection by a woman in the Middle Ages—she is known for a masterpiece of mystical theology, her Libro di divvina dottrina (Book of Divine Teachings), better known today as the Dialogo, a synthesis of her spiritual insights, structured in the form of a dialogue between Catherine and God. It was largely through her Libro, in addition to the hagiographical tradition, that her reputation spread throughout Europe. Catherine became the object of an active cult before her canonization in 1461, and she was embraced in the early modern period as a mystic and model for female monasticism. In the period of Italian nationalism from the Risorgimento through World War II, she became an emblem of Catholic Italy, and more recently she has been valued more for her active engagement with the world as well as for her spiritual writings. Scholars of Catherine of Siena and her devotees—two not-mutually exclusive groups—have over time vacillated radically in their sense of Catherine’s association with Italian politics and society, and in their assessments of her writings and their place in literary culture. Until recently, she has not been taken seriously by Italian literary critical scholarship: the inspired, devotional character of her prose, and its mix of oral with literary characteristics, has seemed to place her outside of literature, properly speaking. But there is currently a renewed interest in Catherine as an author, as well as a return to questions regarding the complexities of her texts and their composition first raised in the initial flowering of Catherinian source criticism in the 1930s and 1940s. She emerged as an important figure in international medieval scholarship with the rise of interest in hagiography, lay spirituality, and women’s religion and gendered religiosity in the last quarter of the 20th century, and is now recognized by historians as a key representative of important trends in late-medieval religion.