Mercurial Natures: Chaucer’s Trans Poetics is the first full-length monograph to bring a trans studies approach to the work of fourteenth-century author and “father of English poetry” Geoffrey Chaucer. It argues that Chaucer looks to the body in transition as a poetic tool to test the boundaries of interpretation. Interpretation is the poetic mode that brings us into relation with another; in Chaucer’s poetry, uncertainty about bodies in transition often leads to interpretative control and hermeneutic violence. Through four chapters and two interstitial fragments, Mercurial Natures focuses on figures who evade interpretative capture by turning away from patristic authority and toward new techniques of knowing, such as the Wife of Bath’s planetary gender or the Yeoman’s counterfeit poetics. Pairing Chaucer’s poetry with literary texts by Gower and Wycliffe as well as vernacular medical and scientific texts by Henry Daniel and Thomas Norton, Mercurial Natures examines the methods of interpretation available to late medieval English thinkers to approach gender as the instrument for relation. By focusing on trans life as a site of meaning-making in Chaucer’s canon, Mercurial Natures puts pressure on the interpretation of bodies while also attending to the porous and relational meaning that “reading” another may offer.