This chapter documents an 1810–1811 epistolary prank in which Percy Shelley outlined his atheistic creed to a completely befuddled correspondent. As this exchange makes clear, Shelley’s writings against theism are attempts to counter dominant eighteenth-century perceptions of unbelief. Indeed, the poet’s letters indicate the influence such perceptions maintained well into the nineteenth century and beyond. Shelley’s promotion of atheism relies not only on logical arguments he derived from previous freethinkers and religious radicals. It also depends on his appropriation and rewriting of the various stereotypes of atheism produced throughout the preceding century. If atheists in the eighteenth century were imagined as selfish, unsociable, and incapable of sensibility, Shelley flipped the script by casting such aspersions on theists themselves.