An advisory opinion, in civil procedure, is an opinion issued by a court that does not have the effect of resolving a specific legal case, but merely advises on the constitutionality or interpretation of a law. Some countries have procedures by which the executive or legislative branches may certify important questions to the judiciary and obtain an advisory opinion.

Countries in which advisory opinions are generally prohibited

United States

The United States Supreme Court has determined that the case or controversy requirement found in Article III of the U.S. Constitution prohibits United States federal courts from issuing advisory opinions. In a letter to President George Washington, replying to the president's request for such an opinion, then-Chief Justice John Jay replied that it would violate the separation of powers for the Supreme Court to provide such an opinion, noting that the president could rely on advice from anyone within the executive branch. Over a century later, in the case of Muskrat v. United States, 219 U.S. 346 (1911)), the Court dismissed a case because there was no actual controversy between the parties; thus, any opinion rendered would be advisory.

Many state courts are similarly barred from issuing advisory opinions, although there are often specific exceptions to these limitations. Some states permit the governor to certify questions on the constitutionality of laws to the state supreme court. Also, some states require their supreme court to give advisory opinions on particular matters, such as whether proposed amendments to the state constitution violate the U.S. Constitution.