‘Improvisation’ is the process of creating dramatic, musical or poetic works at the time of their performance. But extemporisation is not confined to these arts; it is the mundane rule of human responses to the world, which are marked by imperfection and disfluency. What we specially name ‘improvisation’ normally adds fluency, artistry and a degree of difficulty to an utterance or act. Written poetry such as Byron’s can only appear improvised, however in-the-moment it may appear. Opportunities for revision and the hiatus between composition and reception preclude a read poem from the improvised genres. In parts of Don Juan, Byron’s narrator affects the disfluencies of spontaneous speech; but these parts do not in fact resemble the productions of the famously fluent Italian improvvisatori as much as some other sections of Byron’s poetry. The passages that provide the illusion of improvisation most convincingly are those in which disfluency and self-reflexiveness are at their lowest, artistry appears effortless, and the narrator is apparently swept away by the intensity of his thoughts and passions.