Lobbyists frequently join forces to influence policy, yet the success of active lobbying coalitions remains a blind spot in political science research. This study is the first to systematically test how and when characteristics like coalition composition affect lobbying outcomes.

Based on pluralist theory, one might expect diverse coalitions—uniting different societal interests—to effectively signal broad support to policymakers. However, our analysis reveals that this relationship isn't straightforward; it depends critically on Issue Salience.

* Less prominent (or "less salient") issues: Homogeneous coalitions are more likely to succeed here.

* Highly salient issues: Diverse coalitions show higher success rates.

These findings stem from a novel dataset comprising 50 distinct policy issues across five European countries. We employed regression analysis to examine the data and test these pluralist theory predictions, including both the potential signaling benefits of diversity and the cooperation costs it might impose within the group.