This chapter analyzes Jacques Lacan’s influential work ‘Instance of the Letter in the Unconscious, or Reason Since Freud,’ given in 1956 for the Fédération des Étudiants ès Lettres. Lacan derived a theory of the ‘letter’ as an element of concrete discourse borrowed from the structure of language overall. In doing so, he both utilized and critiqued concepts drawn from structural linguistics, particularly the work of Ferdinand de Saussure. Freud’s revolutionary addition, according to Lacan, is the notion of the unconscious, which defines the subject through the operations of condensation (metaphor) and displacement (metonymy). This essay particularly emphasizes the role of rhetoric in Lacan’s work, arguing that because speech is the fundamental medium of psychoanalysis, attention to rhetoric is a vital element of the analyst’s repertoire. Lacan concludes by leveraging his arguments in the context of philosophy, particularly Cartesian concepts of the subject and Heideggerian notions of being. ‘Instance of the Letter’ is a valuable part of Lacan’s corpus for a diverse set of audiences, and forms one of the most important works of his early career.