An amicus curiae (literally, "friend of the court"; plural: amici curiae) is someone who is not a party to a case who assists a court by offering 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. The phrase amicus curiae is legal Latin.
The examples and perspective in this deal primarily with the United States and do not represent a worldwide view of the subject. (March 2020)
In the United States, 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. In other jurisdictions, such as Canada, an amicus curiae is a lawyer who is asked by the court to provide legal submissions regarding issues that would otherwise not be aired properly, often because one or both of the parties is not represented by counsel.