Henry Daniel, fourteenth-century medical writer, Dominican friar, and contemporary of Chaucer, is one of the most neglected figures to whom we can attribute a substantial body of extant works in Middle English. His Liber Uricrisiarum, the earliest known medical text in Middle English, synthesizes authoritative traditions into a new diagnostic encyclopedia characterized by its stylistic verve and intellectual scope. Drawing on expertise from a range of scholars, this volume examines Daniel’s capacious works and demonstrates their significance to many scholarly conversations, including the history of late medieval medicine. It explains the background for Daniel’s uroscopic and herbal work, describes all known versions of the Liber Uricrisiarum and traces revisions over time, analyses Daniel’s representations of his own medical practice, and demonstrates his influence on later medical and literary writers. Both a companion to the recently published reading edition of the Liber Uricrisiarum and a work of original scholarship in its own right, this collection promotes a wider understanding of Daniel’s texts and prompts new discoveries about their importance.