This thesis is a comprehensive account and analysis of the contribution of architect and author A. J. Penty to British social criticism and aesthetic theory. The central argument is that Penty has been neglected in scholarship as the result of an historical misclassification. In the existing literature he is presented as a marginal figure in the history of English guild socialism, a movement his first book did much to inspire. He was, in fact, in conflict with fundamental aspects of the guild socialist movement as it developed. Considered in totality, Penty's views were those of a reactionary conservative, and his significance in early twentieth-century political thought can best be understood by locating him within the essentially Victorian tradition of medievalism, which sought to use the social and economic arrangements of the Middle Ages as a perspective from which to criticise industrial society. The thesis therefore investigates the complex nature of Penty's intellectual debts to earlier thinkers, such as Ruskin, Carlyle, Morris, Carpenter, and Matthew Arnold. A subsidiary contention is that the continuing relevance of medievalism in Edwardian and later intellectual life has been underestimated. Some of its central themes can be discerned in the several political currents with which Penty was in varying degrees associated, such as guild socialism, distributism, Christian social action, agrarian revivalism and fascism. Support for this view has been found by examining Penty's personal and intellectual links with likeminded contemporaries, including Belloc, Chesterton, de Maeztu, Saunders Lewis, T. S. Eliot, Berdyaev and A. K. Coomaraswamy.The thesis aims to highlight the continuities between Penty and his nineteenth-century antecedents and also to identify his original contributions to the development of medievalist thinking, particularly in the sphere of international relations theory. 3 2