This book explores theater history's unexamined importance to Cartesian philosophy alongside Descartes's unexamined impact on theatre history. Put another way, it provides a new reading of mind-body union informed not only by Descartes's Passions of the Soul and his correspondence with Elisabeth of Bohemia but also by stage theory and practice, while simultaneously itemizing the contributions of Cartesianism to this theory and practice. For example, Descartes's coordinate system reshaped theater architecture's use of space—as demonstrated by four iconic theaters in Paris and London, whose historical productions of Racine's Phèdre are analyzed. Descartes's theory of the passions revolutionized understandings of the emotional exchange between spectacle and spectator in general and dramatic catharsis in particular—as demonstrated in Descartes-inflected plays and dramatic theory by Pierre Corneille and John Dryden. And Descartes's philosophy engendered new models of the actor's subjectivity and physiology—as we see not only in acting theory of the period but also in metatheatrical entertainments such as Molière's L'Impromptu de Versailles and the English rehearsal burlesques that it inspired, such as George Villiers's The Rehearsal. In addition to plays both canonical and obscure and the writings of Descartes and Elisabeth of Bohemia, the book's key texts include religious jeremiads, aesthetic treatises, letters, frontispieces, architectural plans, paintings, ballet libretti and all manner of theatrical ephemera found during research in England, France, and Sweden.