This chapter introduces the history of William Blake’s reception as a mystic. It details Blake’s critical reputation from the nineteenth century to the present, and considers why contemporary critics are far less likely to call Blake a mystic than their early twentieth-century predecessors. The chapter demonstrates the critical neglect of women spiritual leaders in mystic and prophetic circles by a number of previous scholars, and considers the wider impact of such academic de-prioritisation on the fields of Romantic and Celtic Modernist studies. This Introduction defines the concepts of mysticism, prophecy, and esotericism used in the rest of the monograph, and details the crossover between the three terms. It also introduces the book’s key figures, placing each in context with the spiritual movements of their times.