In many judicial systems, an advisory opinion is a legal interpretation issued by a court or a commission that does not have the effect of adjudicating a specific legal case between contending parties, but rather advises on the legal dimensions of a situation, such as its constitutionality or legal consequences. Some countries have procedures by which the executive or legislative branches may defer important questions to the judiciary and obtain an advisory opinion in order to guide decisions. However, in other countries or specific jurisdictions, laws may prohibit courts from issuing advisory opinions.

In the international system, with the International Court of Justice (ICJ) as the highest arbiter of between states, as states are the ICJ’s unique clients in contentions cases. However, under Chapter IV of its Statute (an annex to the United Nations Charter) all of the principal organs of the United Nations (except the Secretary-General representing the UN Secretariat), the 16 UN Specialized Agencies and the Interim Committee of the General Assembly may request Advisory Opinions of the ICJ.

Contrary to contentious case judgments, Advisory Opinions have no binding (enforceable) effect, except in rare cases where it is stipulated in advance (e.g., as in inquiries involving the Convention on the Privileges and Immunities of the United Nations and Headquarters Agreements between the United Nations and the United States of America). The requesting UN organ, agency or organization remains free to decide, by any means available to it, to determine what effect to give to the Advisory Opinion.

The Advisory Opinion’s nonbinding character does not mean that it lacks legal effect, because they embody legal reasoning that reflects the Court`s authoritative views on important issues of international law. Moreover, the Court arrives at Advisory Opinions following essentially the same rules and procedures as in its binding judgments in contentious cases submitted by states. Thus, an Advisory Opinion’s high status and authority derive from the fact that it is the official pronouncement of the principal judicial organ of the United Nations.

Read more:

ICJ Advisory Jurisdiction (ICJ website)

ICJ Advisory opinion on the Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory, including in and around East Jerusalem, 9 July 2004

ICJ Advisory opinion on the Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory, including in and around East Jerusalem, 9 July 2004 (summary)

Advisory opinion of the International Court of  Justice on the Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory, including in and around East Jerusalem,” ES-10/15, 2 August 2004;

الفتوى الاستشارية محكمة العدل الدولية بشأن الآثار القانونية عن تشييد جدار في الأرض الفلسطينية المحتلة، بما فيها القدس الشرقية وما حولها، دإط -  ١٥/١٠، 2 آب/أغسطس 2004؛

  الأعمال الإسرائيلية غير القانونية في الأرض الفلسطينية المحتلة والقدس الشرقية، دإط - ١٤/١٠، 12 كانون الأول/ديسمير 2003؛

Illegal Israeli actions in Occupied East Jerusalem and the rest of the Occupied Palestinian Territory, ES-10/14, 12 December 2003;

Pieter H.F. Bekker, The UN General Assembly Requests a World Court Advisory Opinion On Israel`s Separation Barrier, in American Society of International Law, ASIL Insights (December 2003);

ICJ Advisory opinion on the international legal status of Western Sahara, 16 October 1975;

ICJ Advisory opinion on the international legal status of Western Sahara, 16 October 1975 (summary);

International Court of Justice Advisory Opinion on Accordance with international law of the unilateral declaration of independence in respect of Kosovo, 22 July 2010.