Amicus curiae briefs are, in essence, a way for groups that are not actively involved in a case to lobby the court that is deciding the case. In this sense, they are a way to bring a little bit more democratic input into important cases in the legal system.
The judicial branch sometimes decides cases that are of tremendous importance to the country as a whole. In recent times, the Supreme Court has, for example, ruled on the constitutionality of “Obamacare” and the constitutionality of limitations on campaign spending. These are issues that affect everyone.
Because these issues are so important, many groups want to have their voices heard. When issues are in front of Congress, this is easy because interest groups can simply lobby the members of Congress. However, they cannot lobby Supreme Court justices in the same way. This is where amicus briefs come in. They allow interest groups to present their point of view to the court as it tries to make a decision. By doing so, amicus briefs allow the groups to bring up points of law and other information of importance.
Amicus briefs, then, increase the level of public, democratic input into important court cases.