Pamela J. Shoemaker and Stephen D. Reese’s Hierarchy of Influences is a theoretical model that outlines levels of forces affecting media content production. Since its introduction in 1991, the model has proven to be an important framework to study contemporary forms of political communication and the media transformations associated with them. The HoI model is particularly well equipped to examine how media production takes place within a larger organizational, institutional, and ideological context, as it maps the diverse streams of influence into a comprehensive framework. In this encyclopedia entry, the authors summarize the theoretical components of the model and discuss how it has been applied in the study of political communication.