Focusing on the poetry and poetics of four pivotal authors, this book examines how experimental approaches to poetic form in the post-war United States rejected the model of the indivisible subject as the principal locus of artistic creation, and in so doing reframed period-defining questions surrounding the limits and possibilities of human agency. In the decades following the Second World War, poetry in the U.S. was marked by a resurgence of manifesto culture, where practitioners and scholars from a range of political persuasions debated fiercely the common presumptions underpinning the practice and interpretation of poetry. These debates were all primarily concerned with the agency of poetic writing and performance, including what cognitive or affective processes particular formal arrangements can be said to enact within a reader, or how different approaches to the writing and reading of poetry might encourage more desirable modes of acting in the world. Looking specifically at the work of Charles Olson, Langston Hughes, Frank O'Hara and Denise Levertov, this book asks what role poetry plays in conceptualising human agency, and what interdisciplinary place the practice of poetry has within questions typically framed by the disciplines of philosophy and the social sciences.