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, there is a lack of consensus regarding the determinants of party–group connection. This study aims to advance 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 on the strength of the linkage established between parties and interest groups, as well as their determinants. The results suggest that there is a great variation in party–group links, which is explained mostly by party characteristics, namely the type of parties, ideology, and their electoral strength.
