An amicus brief is a legal brief filed in a court case by an individual or organization who is not a party to the case but has a strong interest in the matter. The purpose of an amicus brief is to offer information, expertise, or insight that has a bearing on the issues in the case. The decision on whether to consider an amicus brief lies within the discretion of the court. In American law, an amicus curiae typically refers to what in some other jurisdictions is known as an intervenor: a person or organization who requests to provide legal submissions so as to offer a relevant alternative or additional perspective regarding the matters in dispute.

There are several reasons why an individual or organization may choose to file an amicus brief. These include:

• To set a precedent: Many entities choose to file an amicus brief when the outcome of the case directly affects their members. An amicus brief will allow them to speak to the appellate court on the subject matter at hand and advise the court on how a specific ruling on the case will affect their members and the organization that they are a part of.

• To share knowledge: An individual or organization may file an amicus brief if they have extensive knowledge of a subject and want to educate the judges. This type of brief is usually reserved for field experts and academics who can bring experience to the table.

• To raise a persons profile: An amicus brief can be a good way for a group to relate to the public in such a way that influences goodwill and even profits.

Amicus briefs can be valuable in cases involving an emerging area of law or an issue in which controlling case law is controversial, not in harmony, or nonexistent (cases of "first impression"). They can also address policy or social issues outside the technical limits of the case or that were not addressed by the parties briefs, due to page limits or other considerations.

In summary, an amicus brief is a legal brief filed by an individual or organization who is not a party to a case but has a strong interest in the matter. The purpose of an amicus brief is to offer information, expertise, or insight that has a bearing on the issues in the case. There are several reasons why an individual or organization may choose to file an amicus brief, including to set a precedent, share knowledge, or raise a persons profile.