Interest groups attempt to shape the content of law and policy in a variety of venues, including the legal system. Though the bulk of research dedicated to understanding interest group participation in litigation occurs in the context of the United States, there have been growing efforts to explore this important topic from a cross-national perspective. We contribute to this literature by investigating interest group amicus curiae and intervener activity across 11 English-speaking high courts during the 1969–2002 era. Our results support our theoretical argument that institutional features of courts and nations heavily shape levels of organizational litigation, including the power of judicial review, the rules governing third-party participation, and the presence of a bill of rights. This research informs our understanding of institutional design, social movement litigation, and the democratic nature of courts.