This book reconstructs the theory of signification implicit in Aristotle’s De Interpretatione and its psychological background in his writing De Anima, a project often envisioned by scholars but never systematically undertaken. I begin by explaining what sort of phonetic material, according to Aristotle, can be a significans and a phônê. To that end, I provide a physiological account of which animal sounds count as phônê, as well as a psychological evaluation of the cognitive content of the phônai under consideration in De Interpretatione: names, verbs, and assertive sentences. I then turn to noêmata, which, for Aristotle, are the psychological reference and significata of names, verbs and assertive sentences. I explain what, for Aristotle, are the logical properties a significatum must have in order to be signified by the phonetic material of a name, verb or assertive sentence, and why noêmata can fulfil those logical conditions. Finally, I elucidate the significans-significatum relation without making use of the modern semantic triangle. This approach is consonant with Aristotle’s methodology and breaks new ground by exploring the connection between the linguistic and psychological aspects of Aristotle’s theory of signification.