In addition to serving as instruments of pedagogy and moral instruction, commonplace books helped readers assert control over an ever-increasing quantity of printed material. During the eighteenth century, they were a perfect tool for making reading truly “useful.” Inherently idiosyncratic, the evidence from commonplace books is difficult to generalize; nevertheless, they capture the moment when readers appropriated Enlightenment ideas to address their own concerns. This chapter focuses on Thomas Thistlewood’s commonplace books to track his thinking about race and slavery as well as religion. Initially motivated by the need to learn about plantation management, his reading expanded from planters manuals to works that both promoted and challenged theories of racial difference, urged reform of the institution of slavery, and contained dire warnings of slave rebellions. Thistlewood’s readings on religion combined a deep skepticism of Christian orthodoxy with anxieties about divine justice and a search for personal transcendence, which culminated in his enthusiastic approval of the deism expressed by Jean-Jacques Rousseau’s Savoyard vicar.