This Element develops an analytical framework for understanding the role of ideas in political life and communication. Power in Ideas argues that the empirical study of ideas should combine interpretive approaches to derive meaning and understand influence with quantitative analysis to help determine the reach, spread, and impact of ideas. This Element illustrates this approach through three case studies: the idea of reparations in Ta-Nehisi Coates's The Case for Reparations, the idea of free expression in Mark Zuckerberg's Facebook policy speech at Georgetown University, and the idea of universal basic income in Andrew Yang's Freedom Dividend. Power in Ideas traces the landscapes and spheres within which these ideas emerged and were articulated, the ways they were encoded in discourse, the fields they traveled across, and how they became powerful.