Pre-modern acting theory was framed around emotion, not character, and in this chapter I explore what ‘emotion’ is. There is growing recognition today that emotions have a history, and neurology has suggested new ways of thinking about the mind–body connection. The assumption that humankind has distinct fundamental emotions remains a widely held position today. Passions and emotions: the question of terminology: in addition to the distinction between passions and emotions, I interrogate notions of mind and soul, complicated by questions of translation. Early Modern England: Hamlet seen through the lens of the contemporary Jesuit Thomas Wright, who negotiated competing theories of emotion. The Cartesian turn: I consider Mondory as a pre-Cartesian actor, and the fundamental influence of Charles Le Brun on acting as well as paining. David Hume and English acting theory in the Enlightenment: the multiplication and refinement of emotions as reflected in the theories of Aaron Hill. Two examples of playing the passions: Lekain’s Herod and Nossiter’s Juliet: I draw on Lekain’s manuscript notes and on Morgan’s account of Nossiter’s performance. Rousseau and the ideal of emotional authenticity: Rousseau’s Pygmalion attempted to reconcile the needs of rhetorical delivery with a new sense of emotional truth.