The increase in the percentage of Americans who claim no religious affiliation has sparked renewed debates about processes of secularization. Too often, however, these discussions overlook nonreligious diversity, and all religious “nones” are assumed to be homogeneous. Using the 2014 Pew Religious Landscape Survey, this chapter details the many different ways theistic nonbelief and religious non-affiliation can overlap and diverge. It then uses cluster analysis to condense this diversity into the categories that are the most similar in socio-demographic, political, and religious characteristics. When possible, atheists, agnostics, and non-affiliated thesis should be treated as distinct categories in social surveys. The chapter also provides basic guidelines for researchers about how best to measure, categorize, and analyze nonreligion. Overall, it is imperative for scholars, journalists, and the public more broadly to account for the diversity of secularities when analyzing and discussing patterns and trends in religious non-affiliation.