This study examines the micro-level foundations of how policy responsiveness may come about. Our study builds on the assumption that elected officials’ information source use shapes their policy actions. We analyze the variation in information sources elected officials rely on for agenda-setting and policy formulation, distinguishing between public opinion sources, advocacy sources, and expert sources. Additionally, we examine how elected officials’ public opinion sources vary across individuals, parties, and political systems. Based on a 2015 survey with 345 Members of Parliament in Belgium ...