This chapter argues that John Keats’s revisionary notions of poetry’s expressive capacities are shaped fundamentally by his theatrical experience. Keats is among a generation of poets who came of age after 1800 when theater and theater criticism were reaching their ascendancy. While acknowledging the common assumption that Hazlitt’s Lectures on the English Poets (1818) was a formative text for Keats, I argue that the influence of Kean’s public persona on Keats’s notions of “negative capability” and the anti-egotistical poet has been largely overlooked. Beyond this, Keats’s fascination with Kean’s interruptive acting style—and with the mobile, imaginative, transgressive subject it imagined—shaped his poetry throughout the 1820 volume upon which his canonical reputation rests. Contrasting Keats’s representation of theatrical experience in Lamia to Frances Burney’s more conservative containment of theatrical energies in her 1814 novel, The Wanderer, I argue that Keats’s poem both represents and enacts a scene of “Cockney interruption” that resists progressive notions of personal and national history. This Cockney resistance to narrative—fostered by Keats’s attraction to Kean—in turn shapes the highly figural lyricism of the odes. The chapter, and the book, close with a reading of “Ode on a Grecian Urn.”