Introduction

The doctrine of incorporation stands as one of the most consequential developments in American constitutional law. Through its mechanics, the guarantees enshrined in the Bill of Rights—freedom of speech, the right to bear arms, protection against unreasonable searches and seizures—were made binding upon the states, fundamentally reshaping the relationship between the federal government and the individual citizen. This transformation did not happen overnight, nor did it occur in a vacuum. It was forged through a series of landmark Supreme Court cases and, critically, through the persistent advocacy of outside parties seeking to influence the Court's direction. The amicus curiae, or "friend of the court," brief has served as one of the primary vehicles for this influence. These briefs submitted by non-parties provide the Court with historical analysis, empirical data, and policy arguments that extend far beyond the record developed by the litigants. In matters of incorporation, where questions of historical intent, federalism, and individual liberty collide, amicus briefs have not merely supplemented the arguments of the parties—they have frequently reshaped the very legal frameworks the Court uses to decide these foundational questions.

The Foundation of Selective Incorporation and the Rise of the Amicus

The modern reliance on amicus briefs in incorporation jurisprudence is best understood against the backdrop of the doctrine's own evolution. The story begins with Barron v. Baltimore (1833), in which Chief Justice John Marshall held that the Bill of Rights applied exclusively to the federal government, leaving the states largely unconstrained by its provisions. This understanding persisted until the ratification of the Fourteenth Amendment in 1868, which promised to fundamentally alter the balance of power between the states and the federal government. However, the Supreme Court initially took a narrow view of the Amendment's privileges or immunities clause, famously gutting its potential in the Slaughter-House Cases (1873).

For decades, the Court resisted arguments that the Fourteenth Amendment empowered the federal judiciary to enforce the Bill of Rights against the states. The shift came incrementally, beginning with Gitlow v. New York (1925), where the Court assumed, for the first time, that the First Amendment applied to the states via the Due Process Clause. This marked the birth of the selective incorporation doctrine, a case-by-case approach where the Court would determine whether a particular right was "fundamental to the American scheme of justice" and therefore binding on the states. This framework was formalized in Palko v. Connecticut (1937) and reached its modern apex in Duncan v. Louisiana (1968), which articulated the test for incorporation as whether a right is "fundamental in the context of the criminal processes maintained by the American states."

The Amicus as an Institution

As the Supreme Court began to grapple with the monumental questions posed by incorporation, the practice of filing amicus briefs grew in both frequency and sophistication. The modern amicus brief is governed by Supreme Court Rule 37, which permits any person or entity to file a brief with the consent of the parties or by leave of the Court. The origins of the practice, however, date back to Roman law, where it was common for a disinterested party to advise a court on matters of law. The practice was adopted in English chancery courts and later transplanted to the United States. Initially, amicus briefs were rare and typically filed by the federal government. But starting in the mid-20th century, the practice exploded. Interest groups such as the American Civil Liberties Union (ACLU) and the NAACP Legal Defense Fund recognized the strategic value of submitting amicus briefs in cases testing the bounds of civil liberties. They could frame the issues, present social science data, and advocate for doctrinal changes that the parties themselves might be unable or unwilling to advance. By the 21st century, the filing of amicus briefs had become a standard feature of virtually every major Supreme Court case, and nowhere has their impact been more pronounced than in the incorporation of the Bill of Rights.

The Functional Roles of Amicus Briefs in Incorporation Cases

Amicus briefs serve several distinct and critical functions in cases involving the incorporation of constitutional rights against the states. These functions go beyond simple advocacy and touch on the very nature of how the Supreme Court conducts its business in the context of American federalism.

Supplying Historical and Empirical Evidence

The most powerful role an amicus brief can play in an incorporation case is to supply the Court with evidence that is simply not present in the formal record of the lower courts. Questions of incorporation often turn on historical analysis: what did the Framers of the Fourteenth Amendment intend? Was a particular right considered fundamental at the time of the Amendment's ratification in 1868? The parties to a case are typically focused on the specific facts of their dispute and may lack the resources or expertise to conduct the deep historical research that the Court demands. This is where amici shine. Organizations like the Cato Institute, the Brennan Center for Justice, and legal historians often file briefs that delve into the congressional debates over the 1866 Civil Rights Act, the reports of the Freedmen's Bureau, and the state constitutions in place in 1868. In McDonald v. City of Chicago (2010), the case that incorporated the Second Amendment, amici submitted extensive historical scholarship demonstrating that the right to keep and bear arms was universally understood as a fundamental right necessary to the security of a free state. Justice Samuel Alito's majority opinion explicitly relied on this historical evidence to conclude that the Second Amendment was "fully applicable" to the states.

Illuminating Practical Consequences

Beyond history, amicus briefs are essential for demonstrating the real-world consequences of incorporating a federal right. The Court is acutely aware that incorporating a new right will invalidate thousands of state and local laws, potentially disrupting established practices in law enforcement, corrections, and local governance. Amici representing state governments, law enforcement organizations, and public interest groups provide the Court with a window into these practical stakes. In Timbs v. Indiana (2019), which addressed whether the Excessive Fines Clause of the Eighth Amendment applies to the states, amicus briefs from civil forfeiture reform organizations and criminal defense lawyers provided detailed accounts of how state and local governments had abused civil asset forfeiture laws. These briefs painted a vivid picture of individuals losing their homes, cars, and life savings without ever being convicted of a crime, persuading the Court that the protections of the Eighth Amendment were essential to guard against overreach by state authorities.

Shaping Doctrinal Tests and Standards of Review

In many incorporation cases, the central question is not simply whether a right applies to the states, but what standard of review the Court should apply. Should the Court adopt a rigid historical test, looking only to whether the right was fundamental in 1868? Or should it apply a more flexible "ordered liberty" test that adapts to evolving social norms? Amicus briefs are often where these competing visions are most sharply articulated. Originalist organizations argue for a strict historical standard, while progressive groups advocate for a more dynamic approach. By framing the analytical options available to the Court, amici help to shape the doctrinal landscape that will govern incorporation questions for generations to come. The battle over the proper test for incorporation—whether it should be total, selective, or based on a specific historical methodology—is fought largely through the competing narratives presented in amicus briefs.

Landmark Cases Forged by Friends of the Court

The influence of amicus briefs on incorporation jurisprudence is not merely theoretical. A close examination of landmark cases reveals a direct and often decisive impact on the Court's reasoning and outcomes.

Gitlow v. New York (1925): The Strategic Use of Amicus Advocacy

In Gitlow v. New York, Benjamin Gitlow was convicted under New York's criminal anarchy law for publishing a leftist manifesto. The case presented a clear opportunity for the ACLU to challenge the state law on First Amendment grounds. The ACLU filed an amicus brief in support of Gitlow, arguing that the Fourteenth Amendment's Due Process Clause incorporated the free speech protections of the First Amendment and bound the states. The brief framed the issue not as a narrow question of criminal law, but as a fundamental struggle for democratic governance. While the Supreme Court ultimately upheld Gitlow's conviction on the merits, it accepted the argument that the First Amendment applied to the states. The Court's opinion stated that "for present purposes, we may and do assume that freedom of speech and of the press—which are protected by the First Amendment from abridgment by Congress—are among the fundamental personal rights and 'liberties' protected by the due process clause of the Fourteenth Amendment." This assumption, which opened the door to the entire edifice of selective incorporation, was a direct result of the framing and advocacy provided by the ACLU and its allies.

McDonald v. City of Chicago (2010): The Modern Amicus Landscape

By the time McDonald v. City of Chicago reached the Supreme Court, the amicus landscape had been transformed. Over 20 amicus briefs were filed in the case, representing a broad cross-section of American society. The National Rifle Association (NRA) and the Cato Institute submitted briefs arguing that the original meaning of the Fourteenth Amendment guaranteed the right to keep and bear arms against state interference. The Solicitor General of the United States also filed an amicus brief urging incorporation. But the most influential briefs were likely those that provided the historical evidence Justice Alito needed to build a majority. One key amicus brief, filed by constitutional law scholars, meticulously detailed the historical record showing that the right to bear arms was viewed as a privilege of American citizenship at the time the Fourteenth Amendment was ratified. Justice Alito's majority opinion leaned heavily on this historical evidence to conclude that the Second Amendment applies to the states. The case stands as a powerful example of how amici can supply the Court with the intellectual scaffolding necessary to reach a landmark result.

Timbs v. Indiana (2019) and the Expanding Frontiers of Incorporation

The pattern continued in Timbs v. Indiana, a unanimous decision holding that the Eighth Amendment's Excessive Fines Clause applies to the states. The petitioner, Tyson Timbs, had his $42,000 Land Rover seized by the state of Indiana after he was convicted of selling a small amount of heroin. The vehicle was valued at more than four times the maximum fine for his crime. The Supreme Court's decision was unanimous, but the reasoning was shaped heavily by the arguments presented in amicus briefs. The National Association of Criminal Defense Lawyers and the Cato Institute filed briefs detailing the pernicious effects of civil asset forfeiture, arguing that it had become a widespread tool for state and local governments to generate revenue at the expense of individual rights. The Court adopted this framing, holding that the protections of the Eighth Amendment are "fundamental to our scheme of ordered liberty" and thus applicable to the states. The decision had an immediate and dramatic impact on law enforcement practices across the country.

Ramos v. Louisiana (2020): History and Tradition in the Amicus Role

In Ramos v. Louisiana (2020), the Court struck down Louisiana's practice of allowing non-unanimous jury verdicts for serious crimes, holding that the Sixth Amendment right to a unanimous jury extends to state criminal trials. The case was a direct challenge to the Court's earlier decision in Apodaca v. Oregon (1972), which had allowed non-unanimous verdicts. The amicus briefs in Ramos were instrumental in demonstrating the racist origins of the non-unanimous jury rule. Briefs from the NAACP Legal Defense Fund, the ACLU, and historians documented that Louisiana and Oregon had adopted non-unanimous jury rules in the late 19th and early 20th centuries specifically to dilute the influence of Black and minority jurors. The Court's majority opinion, written by Justice Neil Gorsuch, relied extensively on this historical evidence, concluding that the right to a unanimous jury was deeply rooted in the common law and fundamental to the American conception of justice. The amicus briefs provided the historical context necessary to overturn a long-standing precedent and extend the protections of the Sixth Amendment to every state criminal defendant.

Evaluating the Amicus Contribution to Incorporation

The growing presence of amicus briefs in incorporation cases raises important questions about their overall value to the judicial system. There are both compelling strengths and legitimate weaknesses to consider.

Strengths: Democratic Legitimacy and Institutional Competence

Proponents of robust amicus participation argue that these briefs serve a vital democratic function. Incorporation decisions are among the most consequential a court can make, because they apply federal constitutional constraints to state and local governments. It is essential that the Court has the fullest possible picture of the potential consequences of its decisions. Amicus briefs ensure that the voices of those most affected—state law enforcement officers, local prosecutors, civil liberties advocates, and ordinary citizens—are heard. They also enhance the Court's institutional competence by providing specialized expertise that the parties may lack. A brief from a historian on the original meaning of the Privileges or Immunities Clause, or a brief from a police chief explaining the practical implications of a new search and seizure rule, gives the Court information it simply cannot get from the briefs of the parties alone. In this sense, the amicus system transforms the Supreme Court into a more informed and more democratic institution.

Weaknesses: Information Overload and Resource Inequality

Despite these benefits, there are significant concerns about the role of amicus briefs in shaping constitutional law. The sheer volume of amicus filings in major cases can overwhelm the Court and the parties. In some cases, the majority of the briefs simply repeat the same arguments, adding little to the debate. Critics also point to the problem of resource inequality. Well-funded interest groups and wealthy corporations can afford to hire the best lawyers and produce polished, high-impact amicus briefs. Under-resourced parties, such as individual criminal defendants, rarely have the same level of amicus support. This creates a structural imbalance in the information presented to the Court, potentially tilting the scales toward well-resourced litigants. There is also a concern about the increasing professionalization of the amicus bar, where elite lawyers in Washington, D.C., produce briefs for paying clients, raising questions about whether amicus advocacy is truly serving the interests of justice or simply functioning as another form of high-cost legal lobbying. The Court itself has expressed frustration with the quality and quantity of amicus briefs, occasionally admonishing lawyers for filing briefs that are merely repetitive or that fail to provide unique value.

Conclusion

The relationship between amicus briefs and incorporation jurisprudence is one of profound and enduring synergy. The doctrine of incorporation requires the Court to make deeply informed judgments about the meaning of liberty, the structure of federalism, and the lessons of history. Amicus briefs provide the raw material for those judgments, supplying the historical evidence, the policy analysis, and the real-world context that the Court needs to decide these monumental cases. From the ACLU's strategic brief in Gitlow to the flood of scholarship submitted in McDonald, friends of the court have repeatedly demonstrated their ability to shape the development of constitutional law. While the amicus system is not without its flaws—including the risks of overload, repetition, and unequal access—its overall impact on incorporation jurisprudence has been overwhelmingly positive. As the Court continues to confront questions about which rights are fundamental to our scheme of ordered liberty, the amicus brief will remain an indispensable tool for ensuring that the justices have the wisdom and information necessary to fulfill their constitutional duty. The continuing dialogue between the Court and its friends is a defining feature of American constitutionalism, and it will continue to shape the meaning of the Bill of Rights for generations to come.