“Race in a Godless World” examines the racial thought of atheists in Britain and the United States from about 1850 to 1914. While there have been no comprehensive studies of atheists' views on race, there is a trend in the historiography on racial thought, which I have described as the “Race-Secularization Thesis,” that suggests a link between the secularization in the eighteenth and nineteenth centuries and an increase in nineteenth-century racialism – that is, racial essentialism and determinism – as well as resulting racial prejudice and discrimination. Through a study of both leading and lesser-known atheists and freethinkers, I argue that the “Race-Secularization Thesis” needs to be reconsidered. A simple link between secularization and racialism is misleading. This is not to suggest that the “Race-Secularization Thesis” contains no truth, only that secularization did not inevitably lead to racialism. This dissertation helps to tell a more complex and nuanced story about the relationship between atheism and racial thought. While in some cases, nineteenth-century atheists and freethinkers were among the leading exponents of racialist views, there is an alternative story in which the atheist worldview – through its emphasis on rationality and skepticism – provided the tools with which to critique ideas of racial prejudice, racial superiority, and even the concept of race itself.