The subject of Public Opinion is structured in four main topics grouped under two greater parts. The first part, which includes Units 1 and 2, will provide an integrative, critical and interdisciplinary approach to the concept of public opinion and to the most important perspectives for understanding it (normative, critical, empirical...). And will end by reviewing the increasing relevance of mass media in early 20th century and the birth of mass communication research related to the study of media effects on public opinion. This last point will serve as a link to the second part, which includes Units 3 and 4. Part 2 takes a more communication-oriented perspective and includes the study of the principal theories dealing with the relationship between media and public opinion and the discussion on the main issues regarding the articulation of public opinion in the digital public sphere. Thereby, it is intended that communication students are able to critically reflect on liberal democracies and on the relationships established between institutions, (mainstream and online) media and citizens and understand the effects the practise of their profession may have on the public, as well as their own relationship with power.