The explicit morality of melodrama and the hieratical organisation of the profession both demanded of its actors unambiguous characterisation and overt emotional expression. This tended to produce stereotypes, social and psychological, while expression drew on all the physical virtuosity of what George Henry Lewes described as ‘the symbols of the actor’s art’. This chapter relates the performer’s presence, gesture, and vocal expression as prescribed in acting manuals (e.g., Henry Siddons, Charles Bell, Henry Neville, and Gustave Garcia) to the psychology, science, and philosophy of the period, from Descartes’s Passions of the Soul to Diderot’s Paradox and Darwin’s Expression in Man and Animals. Particular attention is drawn to the theory and practice of François Delsarte. Acting in melodrama had to complement (or compete with) scenic spectacle and musical accompaniment. With the introduction of scenic naturalism later in the nineteenth century, extravagant gesture gave way to evocative stage business, but the need for unambiguous clarity of feeling and motivation remained. This is exemplified in the performance of Henry Irving in The Bells.