How do readers approach the enigmatic and unnavigable modernist long poem? Taking as the form's exemplars the highly influential but critically contentious poetries of John Cage and Charles Olson, this book considers indeterminacy – the fundamental feature of the long poem – by way of its analogues in musicology, mycology, cybernetics and philosophy. It addresses features of these works that figure broadly in the long poem tradition, such as listing, typography, archives, mediation and mereology, while articulating how both poets broke with the longform poetic traditions of the early 1900s. Brendan C. Gillott argues for Cage’s and Olson’s centrality to these traditions – in developing, critiquing and innovating on the longform poetics of the past, their work revolutionized the longform poetry of the 20th and 21st centuries.