Despite the development of empirical research on the relations between parties and interest groups, the topic is still understudied and presents several shortcomings. On the one hand, this relationship has been studied mostly from the political parties’ point of view. On the other, the role of interest groups as actors of intermediation has been subordinated to the institutional role played by partisan actors. This paper aims to contribute to advancing our knowledge on the topic by examining the relationship between interest groups and political parties in Southern European countries (Greece, Italy, Portugal and Spain). By relying on new data collected through an expert survey, we focus specifically at three different dimensions, namely the type of linkage established between parties and interest groups; the rationale (i.e. aims) of the linkage and the institutional impact of this relationship. From this viewpoint, it will be possible not only to identify different modalities of interest group access to the institutional arena across countries (and parties), but also to provide a fresh look of the intermediation role performed by both actors. Overall, this study contributes to investigating how contemporary democracies perform interest representation and to discussing the emergence of ‘advocacy’ democracy. In addition, the findings are of great relevance for a better understanding of the system of interest intermediation and the functioning of political systems in the twenty-first century.