This thesis examines the hollow-earth theories of John Cleves Symmes and seeks to recognise and restore both his memory and his legacy. I outline Symmes’ theory that the Earth is hollow and habitable within, and accessible via holes at the North and South Poles, consider the impact of this theory on the commencement of the United States Antarctic Exploration program, and demonstrate its lasting legacy within the genre of Symmesian hollow-earth fiction. Previous scholarship has been intermittent, disparate and oddly contextualised, often assigning both Symmes and his theory to the world of the “weird and wonderful.” In order to study Symmes’ legacy, I synthesise previous scholarship and show the continuing presence of his theory – at times unrecognised and unacknowledged – in fiction. Commencing with a description of the series of publications in which Symmes publicised his idea, this thesis looks at his theory’s reception, with a discussion of several books and letters published in response to the theory – from contemporary times through to the current day. In determining the legacy of his theory, rather than the theory itself, I look at possible and probable sources for Symmes’ idea, and place it on the continuum of natural philosophy and science from the thirteenth century so as to set Symmes’ announcement in the perspective of its time. I then address Symmes’ influence on the United States Congress, which culminated in the United States Exploring Expedition of 1838-1842. Finally, I examine Symmes’ legacy in fiction, commencing with an extensive discussion of Symzonia, which some posit was authored by Symmes, and continuing through to the present. I find that while Symmes’ theory, and the ensuing debate about a hollow earth, may have advanced the speed with which the United States commenced Antarctic exploration, with time this exploration would probably have happened anyway. His greatest legacy is through the establishment of a body of hollow-earth fiction based around the fictional hole which now bears his name; “Symmes’ Hole” lives on in literature to the current day.