Who Speaks to the Court? The Amicus Eco­system and Its Impact on U.S. Supreme Court Decision-Making

Contemporary U.S. Supreme Court practice confronts unprecedented outside advocacy, with nearly 2,000 amicus curiae (“friend of the court”) briefs filed annually. Comprehensive analysis spanning over a century reveals systematic patterns: a small oligopoly of repeat-player organizations dominates participation, forming stable coalitions that align or oppose each other with remarkable consistency across cases. Business-conservative, civil-rights-progressive, government, and libertarian blocs supply untested empirical assertions on contentious policy questions—abortion’s effects, educational outcomes, regulatory costs—that embed contested premises into constitutional doctrine. The findings illuminate structural risks to judicial fact-finding and propose calibrated reforms balancing access with reliability safeguards for high-stakes adjudication.