The theoretical reflection on ideology expands with the history of left-wing thought. At the same time, the concept of ideology defines the field of social sciences in its specificity, both from the perspective of the object and that of the subject. Based on these assumptions, this lecture series aims to explore the term, on the one hand, with reference to its partially invisible trajectory between contemporary theoretical approaches, and on the other hand, regarding its distinctive role in modern thought in general. For the first, special emphasis is placed on the work of a thinker who explicitly distanced himself from the term "ideology," namely Michel Foucault. And for the second, the genealogical significance of the term in Marxism is studied, starting from its use in the early work of Marx and Engels, The German Ideology.