Amicus Brief

In a court case, there are normally two sides facing each other: whoever is suing and whoever is being sued. Only these two are allowed to present their arguments to the court. An amicus brief breaks this rule. It allows someone who is not even involved in the dispute to nevertheless file a written submission. The name comes from Latin: “amicus curiae” means “friend of the court.” This refers to someone who provides the court with knowledge that the two disputing parties do not have or do not wish to mention.

Why tech companies weigh in on other people’s lawsuits

In the United States, court rulings carry weight far beyond the individual case. Once a high court decides that a certain practice is unlawful, later proceedings follow that precedent. A dispute between two small companies can thus reshape an entire industry. This is precisely why companies that formally have nothing to do with a case get involved.

This is especially visible in lawsuits over artificial intelligence. Authors, newspapers, and music publishers are suing AI companies because their models were trained on copyrighted text and images. How these cases turn out will determine the business model of an entire industry. So large technology companies, libraries, civil rights groups, and research institutes file amicus briefs to lay out their views.

An amicus brief is not a neutral expert opinion. Whoever files one almost always pursues their own interest. It is more of a publicly viewable attempt to persuade a court. Judges are not obligated to read or take such submissions into account.

From the motion to the footnote in the ruling

The process is strictly regulated. Anyone wishing to file an amicus brief usually needs the consent of both parties to the dispute or permission from the court. There are hard deadlines and length limits — at the U.S. Supreme Court, for instance, around 9,000 words. It must also be disclosed who paid for the brief. This rule is meant to prevent a party to the case from secretly smuggling in additional submissions through proxies.

In terms of content, a good amicus brief does not repeat the arguments of the party it supports. Its value lies in what the parties themselves cannot provide: technical explanations, market data, historical comparisons, or impact assessments. An association of AI developers, for example, explains to the court how a language model actually processes training data. Such explanations occasionally turn up verbatim in judicial opinions later on.

The amicus brief should not be confused with an intervention. Someone acting as an intervenor becomes an actual party to the proceedings and may file motions. An amicus may only write. They file no motions, call no witnesses, and cannot lodge an appeal.

How amicus briefs show up in AI news

The term comes from Anglo-American law and you will mainly encounter it in reports on U.S. proceedings. In German news it often appears untranslated, sometimes as “Amicus-Schriftsatz.” There is hardly a German equivalent, though the Federal Constitutional Court does obtain statements from associations and experts. The function is similar, but the procedure is different.

In AI coverage, amicus briefs regularly appear in copyright lawsuits against model providers, as well as in disputes over platform liability and chip export rules. Reports then read something like: “Several research institutions are supporting the defendant with an amicus brief.” This is a signal of how an industry assesses a legal dispute.

For you as a reader, these submissions are useful because they are publicly accessible. They often explain technical matters more clearly than the case files themselves. What remains important: an amicus brief reveals a set of interests, not the truth. Who stands behind a submission is therefore often more interesting information than its content.