Through his writings opposing cruelty to animals and his vision of a utopian society infused with equality, social justice, and spirituality that begins with an individual’s diet, the Romantic poet Percy Bysshe Shelley influenced generations of reformers and vegetarians. This essay examines his philosophy as embodied in his own alimentation. It answers for the first time the questions of why he devoted so much of his pamphlet A Vindication of Natural Diet (1813) to health and illness, how he could become a vegetarian, and what caused him to lapse from a vegetable diet. It utilizes the concept of “personal food system” to discuss Shelley’s enactment of his identity through daily eating habits. This study also briefly assesses the behaviors of two of Shelley’s friends who sometimes partook of a vegetable regimen, fellow poet Lord Byron and the barrister T. J. Hogg who authored a biography of Shelley, demonstrating further the usefulness of the theoretical framework and indicating more fully why Shelley became the doyen of nineteenth-century vegetarianism. Personal food system, the subject of model building for several years, has rarely if ever been applied to a particular individual, much less an historical personage. This study adds a new dimension to the literature on Shelley, contributes to folkloristics in its attention to custom, belief, and foodways, and reveals how identity may be enacted in a person’s eating behavior.