In nearly every Twelver Shiʿi place of worship, one finds prayer books filled with supplications (duʿāʾ) addressed to God and visitational devotions (ziyārāt) dedicated to the Prophet and his family. This book argues that this literature is not only devotional but among the tradition’s most important intellectual and theological sources. Tracing their transmission from the age of the Imams to the modern period, it reveals how liturgical texts preserved and transmitted ideas about authority, salvation, and communal identity. By bringing prayer literature into the center of Islamic intellectual history, this study uncovers a rich devotional archive through which generations of Shiʿis understood God, the Imams, and the meaning of religious life.