Summary: The approximately 1000 word entry traces the increasing importance of the term from the enlightenment to the present, and focuses on the conflict between the scientific positivist ideal of norm-free understanding and the subjective and prejudice human nature. While the enlightenment established the ideal to study political, social, cultural, and economic issues with positive natural science logic, the entry highlights arguments that view human reason necessarily to be ideologic that is subjective. Both Bacon and Marx argue that ideologies are adhered to and spread for group interests, while Marx highlights that ideologies are the structural expression of capitalist exchange relations. The positivist ideology school, founded by Pareto and developed by Geiger, and the sociology of knowledge school founded by Mannheim problematizes the possibility to make true inferences about the world given the scientists personal, historical, and cultural ideological orientation. The entry argues that constant self-reflection of the scientist s ideological position is critical in the social sciences. The entry ends with a summary of contributions by critical theorists which give up the separation of societal reality and ideological superstructure and instead highlights the constant interaction between the two levels.