Amicus curiae briefs are deeply woven into the fabric of modern federal appellate practice. Indeed, amici curiae submit briefs in approximately ninety percent of the cases that the United States Supreme Court entertains, and the Justices deny a minuscule number of amicus requests to participate. Amicus practice is less ubiquitous in the United States Courts of Appeals. Amici seek to file comparatively few briefs, nearly all of which the appellate courts permit, while many tribunals have not developed a comprehensive jurisprudence for resolving amicus motions. Nonetheless, the United States Court of Appeals for the Seventh Circuit has articulated rather stringent criteria, which it has strictly applied to limit amicus involvement, even as the Third Circuit has formulated less restrictive standards that the court has generously enforced to facilitate amicus participation. The significance of federal appellate court amicus practice will only grow as the twelve regional circuits increasingly become the courts of last resort for their geographic areas because the Supreme Court hears so few appeals. These propositions mean that federal appellate court disposition of amicus curiae motions warrants assessment, which this Article undertakes, concluding that the appeals courts should generally follow the Supreme Court and Third Circuit approaches as illuminated by certain aspects of the Seventh Circuit treatment.