This book examines a selection of high and late medieval Arthur romances, engaging sustainability studies to show the consequences for the Arthurian court's excessive and wasteful practices. It expands the scope of sustainability studies by braiding together the more commonly understood environmental sense of resource allocation and conservation with the idea of sustaining as dynastic continuation: to prolong or maintain a society or a lineage. Together, these strands of sustainability reveal a concerning paradox: the various ways that the Arthur legend is unsustainable--the excess and waste-driven practices of the court, the collapse of the Round Table, and the Grail Quest as achievable only through death--are what sustain the legend. Arthurian texts proliferate, pushing against the already-established birth and death of the king by endlessly expanding the story in between like an over-large literary balloon. This proliferation, and centuries of audience attraction to it, show a problematic desire for this world to subsist beyond its pre-written ending, revealing our love for the excesses and self-defeating grandeur of Arthur's world as a marker of our resistance to change.