How Legitimate are Interest Groups? A Systematic Review and Research Agenda

While legitimacy is a foundational concept in political science, its application to the study of interest groups remains underdeveloped compared to the extensively debated notion of influence. Existing scholarship has focused on groups mobilisation, strategies, access and their impact on policy outcomes, leaving interest group legitimacy largely unexplored, at least in a direct and explicit way. This gap is further reinforced by the lack of clear analytical frameworks, limited cumulative conceptual development, and the absence of a comprehensive overview of the issue within the literature. This article addresses this gap through two objectives. First, it systematically reviews how the concept of legitimacy has been mobilised in interest group research. Following the PRISMA statement and drawing on a corpus of peer-reviewed articles selected through keyword-based queries, we screened 3,273 articles from five major databases to identify those addressing specifically interest group legitimacy. We document the definitions, theoretical approaches, and empirical strategies employed to study legitimacy. We distinguish between normative approaches, which evaluate legitimacy against predefined (democratic) standards, and subjective approaches, which examine how interest group legitimacy is perceived by different actors such as policymakers, group members, or citizens. Normative studies often rely on criteria such as transparency, representativeness, accountability, and the capacity to act as a ‘transmission belt’. However, such studies do not address the crucial question of ‘legitimate to whom and on what basis?’, a question that subjective approaches tackle by empirically exploring perceptions of interest group legitimacy across audiences and contexts. Second, building on the findings of the systematic literature review, we propose a research agenda to advance the study of interest group legitimacy. This agenda also proposes to link legitimacy to other core issues in the scholarship, such as group mobilisation, organisational survival, strategies, and policy influence. We argue that understanding interest group legitimacy is particularly relevant in contemporary governance settings characterised by multi-level decision-making, the erosion of party representation, and the growing role of interest groups as intermediaries between society and public institutions. Methodologically, the article combines quantitative and qualitative analysis of the literature to identify blind spots and future directions. We advocate for greater integration of normative and subjective approaches, as well as comparative research across policy domains and political systems. By clarifying conceptual ambiguities and proposing analytical linkages, this article seeks to reposition legitimacy as a central concern in interest group scholarship and to foster cumulative theoretical development in this field.