An advisory opinion of a court or other government authority, such as an election commission, is a decision or opinion of the body but which is non-binding in law and does not have the effect of adjudicating a specific legal case, but which merely legally advises on its opinion as to the constitutionality or interpretation of a law. The International Law Association is one such commission that provides non binding opinions and advisory documents regarding aspects of international law. Some countries have procedures by which the executive or legislative branches may refer questions to the judiciary for an advisory opinion. In other countries or specific jurisdictions, courts may be prohibited from issuing advisory opinions.

The International Court of Justice is empowered to give advisory opinions under Chapter IV of its Statute (an annex to the United Nations Charter) when requested to do so by certain organs or agencies of the United Nations. These opinions are non-binding.

The advisory function of the Inter-American Court of Human Rights enables it to respond to consultations submitted by agencies and member states of the Organization of American States regarding the interpretation of the American Convention on Human Rights or other instruments governing human rights in the Americas. It is also empowered to give advice on domestic laws and proposed legislation, and whether or not they are compatible with the Convention's provisions.

The High Court of Australia is prohibited by the Constitution of Australia from issuing advisory opinions; a binding determination requires a controversy between two or more parties. There have been occasions in Australia's legal history, such as the 1975 Australian constitutional crisis, when politicians have solicited informal advice from Justices of the High Court in their personal capacity.

Under Canadian law, the reference question mechanism is equivalent to an advisory opinion.

The Supreme Court Act gives the federal Cabinet the power to refer questions to the Supreme Court of Canada on any questions of law. The Supreme Court then has jurisdiction to hold a hearing on the reference, just like an appeal. The Attorney General of Canada participates in a federal reference. The provincial and territorial Attorneys General have the right to intervene, and interested parties may apply to intervene. The parties make detailed written submissions to the Court, which then holds a hearing. It typically reserves its decision, later releasing a written opinion. The Court has a discretion to refuse to answer questions which are too ambiguous or will not provide an answer with any meaning.

The Provincial governments and some of the territories have a similar power to refer questions to their highest appeal courts for an opinion. This power is set out in their respective provincial laws defining the powers of the appellate courts. The Supreme Court Act gives an automatic right of appeal from a reference decision of a provincial Court of Appeal to the Supreme Court of Canada.

In India, the President of India can request the Supreme Court of India to provide its advice on certain matters. This procedure is called "Presidential Reference". According to Article 143 of the Constitution of India, the President of India may refer to the Supreme Court of India, a question of law or fact which, he thinks, is of public importance. It is not binding on the Supreme Court to answer questions raised in the reference. For an analysis of this provision, see noted Indian lawyer Deepaloke Chatterjee's widely cited article on this point