If a case may have effects on other parties, then they may file amicus curiæ briefs. For example, if a decision will affect an entire industry, even though it is brought up against only one company, other companies may file briefs as amicus curiæ. Similarly, if a law in one state is under evaluation, and another state has a law that would be affected by the decision, then this other state may file a brief as an amicus curiæ.

Occasionally, however, amicus curiæ are not opinions on the argument or on one part of the argument, but simply an academic persepctive. For example, if the law gives deference to a history of legislation of a certain topic, a historian may choose to evaluate the claim using his expertise. An economist, statistician, or sociologist may choose to do the same.