Summary: In about 1500 words, the entry traces the understanding of the term from the Romans and Greeks through the Middle Ages to the twentieth century, focuses on the sociological and political science contributions Max Weber inspired, and ends with a discussion of the treatment of power by system-theorists. Early on Greek and Roman authors understood the term power primarily in a constitutional-political context, while no clear separation to neighboring concepts terms such as violence was achieved. As the entry shows, the terms power and violence move closer together in the middle ages, and classical-modern authors such as Machiavelli and Hobbes began to discuss power outside the constitutional context of legitimate power. From then on, power is no longer mainly understood as something only states possess but individuals utilize also in non-political contexts to make others do what they normally would not have done. Marx and Engels , for example, criticized the power relationships in the economic realm. As the entry points out, Weber developed a rather open definition of power. That inspired political scientists to attempt to develop typologies of power resources, possibilities when to strategically apply those resources, differences in societal areas (politics, economy, parties, interest groups, military, church etc.) and levels of analysis (from local to international). Specific conceptions such as structural and negative power as well as non-decisions are discussed. The entry ends with a substantive discussion of contributions from system theorists - such as Parsons, Deutsch and Luhman - to the development of a general theory of power, and a call for empirical studies to establish the relevance of system-theoretic approaches.