Abstract: This dissertation explores the role of mens rea, or guilty mind, as a factor in jury assessments of guilt and innocence during the first two centuries of the English criminal trial jury, from the early thirteenth through the fourteenth century. Drawing upon evidence from the plea rolls, but also relying heavily upon non-legal textual sources, including popular literature and guides for confessors, I argue that mind was central to how jurors determined whether a particular defendant should be convicted, pardoned, or acquitted outright. I analyze the meaning of the word “felony,” demonstrating that its meaning was considerably more complex in the medieval context than it is now, when it tends to serve as a placeholder for a category of serious crime. An examination of the word’s use in medieval England’s three primary languages—Latin, Middle English, and Anglo-Norman French—reveals that “felony” was often used interchangeably with such concepts as malice, iniquity, treason, and evil. Furthermore, jury acquittals and pardon recommendations reveal a default understanding of felony that involved, in its paradigmatic form, three essential elements: an act that was reasoned, willed in a way not constrained by necessity, and evil or wicked in its essence. Further chapters explore the complicating role of anger, which could exacerbate or reduce the level of guilt attached to an alleged felony; the contours and mechanisms of guilt assessment, including the gradation of particular sins and crimes and the use of confession to access guilty mind; and the peculiar dangers and difficulties involved in the task of judging, a task shared by judges and jurors within the medieval English system of felony adjudication. The dissertation engages with a long-standing discussion on the history of the medieval English criminal trial jury while also initiating a new discourse on this early chapter in the long Anglo-American history of ideas about criminal responsibility. It introduces a new methodological approach for the study of the early criminal trial jury, placing legal texts within a broader cultural context in order to illuminate the concerns of jurors otherwise largely silenced by the formality and brevity of the legal record.