Agenda-Setting and Gatekeeping Theories in the Digital Age of Algorithmic Media: A Critical Synthesis Review and Theoretical Extension (2000–2025)

The parallel evolution of agenda-setting and gatekeeping theory constitutes one of the most consequential intellectual trajectories in communication studies, yet the two traditions have developed largely in isolation from each other despite their deep functional interdependence. This paper undertakes a critical, integrative review of both traditions across the period 2000 to 2025, a quarter-century defined by the migration of public discourse from institutionally controlled media environments to algorithmically mediated digital platforms. Drawing on a structured synthesis of peer-reviewed scholarship, including the landmark platform-experiment literature of 2021–2025, the paper traces the transformation of gatekeeping from a process enacted by identifiable human decision-makers within institutional hierarchies to a distributed, computationally governed phenomenon in which algorithms, platform architectures, and user behaviors jointly determine the visibility of information. Simultaneously, it examines the reconfiguration of agenda-setting from a linear transfer of salience between media institutions and mass publics to a recursive, networked process shaped by personalization technologies, platform-specific affordances, and the fragmentation of formerly unified audiences into algorithmically constituted micro-publics. The paper introduces the concept of salience agency as an integrative meta-theoretical framework capable of capturing the convergence of gatekeeping and agenda-setting within contemporary communication systems. It argues that the algorithmic mediation of information visibility represents not merely a technological augmentation of existing communicative processes but a structural transformation that demands new theoretical vocabularies, new empirical methodologies, and new normative commitments. Implications for communication scholarship, media management, regulatory policy, and democratic governance are discussed, and priorities for future research are identified.