The word "spirit" appears in discipline's leading journals more often than other expressions associated with religion like "Christianity," "religion," and "faith." Yet, despite its ubiquity, it is unclear how or why the term is used in social science analysis. What do political scientists talk about when they talk about the spirit? Answering this question has important implications for conceptual clarity, for the study of religion in the discipline of political science, and for mapping the influence of religion on the discipline of political science. The article answers this question through a conceptual genealogy of the term "spirit" in the publications of classical, modern, and contemporary scholars, alongside a quantitative content analysis using a novel data set. For classical scholars, the concept of the spirit repurposed the Christian Holy Spirit to advance Enlightenment theories about human progress. For modern and contemporary scholars, the spirit was further scrubbed of Christian connotations and inscribed with liberal idealist commitments to freedom. When political scientists talk about spirit, they reveal a theoretical indebtedness to the Christian concept of a transcendent and intangible force that animates, directs, and guides humans. American political science's continued entanglement with liberal Protestantism has made the discipline's emphasis on liberal democracy appear natural and given rather than particularistic. Furthermore, explicating American political science's entanglement with liberal Protestantism helps to explain longstanding gaps in knowledge and systematic exclusions.