The document discusses the concept of agenda setting in mass media. It defines agenda setting as the process by which mass media determines what issues the public thinks and worries about. The media influences public agenda by choosing what news to report on and how prominently to feature different issues. This public agenda then influences policy decisions. The document traces the origins of agenda setting theory to Walter Lippmann in the 1920s and its formal development by McCombs and Shaw in the 1960s. It also outlines how agenda setting occurs in three levels - the media agenda, public agenda, and policy agenda.