This study sets out to reveal the groundbreaking use of monody in the late plays of Euripides: in his hands, it is shaped into a potent and flexible instrument for representing emotion and establishing new narrative and thematic structures. Engaging with the current scholarly debate on music, affect, and characterization in Greek tragedy, I examine the role that monody plays in the musical design of four plays of Euripides, all produced in the last decade of his career: Ion, Iphigenia in Tauris, Phoenician Women, and Orestes. These plays are marked by the increased presence of actors’ song in proportion to choral song. The lyric voice of the individual takes on an unprecedented prominence with far-reaching implications for the structure and impact of each play. The monodies of Euripides are a true dramatic innovation: in addition to creating an effect of heightened emotion, monody is used to develop character and shape plot. In Ion, Iphigenia in Tauris, Phoenician Women, and Orestes, Euripides uncouples monody’s traditional and exclusive connection with lament. In contrast to the work of Aeschylus and Sophocles, where actors’ song is always connected with grief and pain, in these four plays monody conveys varied moods and states of mind. Monody expresses joy, hope, anxiety, bewilderment, accusation, and deliberation. Often, and simultaneously, it moves forward narrative exposition. The scope and dramatic function of monody grows and changes: passages of actors’ lyric become longer, more metrically complex, more detached from the other characters onstage, and more intensely focused on the internal experience of the singer. In the four plays under discussion we see a steadily increasing refinement and expansion of the form, a development that rests upon the changes in the style and function of contemporary music in the late fifth century. By 415 B.C., many formal features of tragedy had become highly conventionalized, and determined a set of expectations in the contemporary audience. Reacting against this tradition, Euripides successively redefines monody: each song takes over a traditional Bauform of tragedy, and builds upon it. The playwright uses the paired monodies of Ion to pose a conflict of ideas that might otherwise be conveyed through an agon. In Iphigenia in Tauris the heroine’s crisis and its resolution are presented in lyrics, rather than as a deliberative rhesis. In Phoenician Women, Antigone, Jocasta, and Oedipus replace the Chorus in lamenting the fall of the royal house. Finally, the Phrygian slave in Orestes sings a monody explicitly marked as a messenger speech that inverts the conventions of the form to raise questions about objectivity and truth in a disordered world. In examining these four plays, I hope to show some of the various potentials of this new Euripidean music as a major structural element in tragic drama, insofar as it can heighten emphasis, allow for the development of emotional states both subtle and extreme, reveal and deepen character, and mirror thematic movements. Euripides establishes monody as a dramatic form of considerable versatility and power. The poetry is charged with increased affect and expressivity; at the same time it articulates a new self-consciousness about the reciprocal capacities of form and content to shape one another. Here we may discern the shift of sensibility in Euripides’ late work, which proceeds pari passu with an apparent loosening of structural demands, or what one with equal justice might recognize as an increase in degrees of freedom. As the playwright repeatedly reconfigures the relationship between form and content, the range of what can happen onstage, of what can be said and sung, expands.