Amicus briefs occupy an unusual place in appellate litigation. They are filed by outsiders, yet they can supply technical knowledge, historical material, institutional perspective, or arguments the parties have not developed. Public discussion of the practice remains centered on the Supreme Court. Far less is known about the federal courts of appeals, even though those courts resolve tens of thousands of matters and frequently provide the last word in nationally significant disputes.
This post uses a new dataset of 2024 federal appellate decisions provides a systematic account of that practice across the 12 regional circuits. It identifies 576 case families with proven amicus participation and links 1,521 confirmed briefs to 460 of those families. The other 116 families contain reliable evidence that amici participated, but individual brief records could not be reconstructed. The data therefore supply a comprehensive family-level universe and a conservative lower-bound account of briefs, filers, and coalitions.
The data also permit a closer look at what happens after a brief is filed. A broad text screen flagged 176 families for possible engagement and 95 for a possible brief citation. Those screens deliberately favored recall and included false positives. A completed manual audit of the 21 strongest exact-link candidates found substantive engagement in 18 cases, mere acknowledgement in two, and a reference to a brief from a prior appeal in one. The results show why filing, citation, and influence must remain separate concepts.