Even if democratic theory expects interest groups to act as important transmission belts between the public and the political system, there is a lack of empirical literature linking public opinion and interest groups. The aim of the paper is to examine the potential of interest groups to act as a transmission mechanism between public opinion and policy by comparing the policy positions of interest groups and the public. In order to do so we have collected a new original dataset linking public opinion and policy positions of interest advocates on altogether 50 policy issues in Denmark, Germany, the Netherlands, Sweden, and the United Kingdom. The first part of the paper theorizes about the conditions under which the policy positions of individual advocates and the general public are similar. It tests whether there are systematic differences in the degree of congruence between different types of advocates, such as those representing diffuse and specific interests. Moreover, it considers whether characteristics of the issues on which groups mobilize can help account for varying levels of policy congruence between individual groups and the public. The second part of the analysis looks at congruence between public opinion and advocates at the policy issue level with the aim of exploring whether there is variation in such congruence between different types of policy issues, issues representing different levels of salience as well as between issues debated in countries with different state-society structures.