The International Court of Justice has jurisdiction in two types of cases: contentious cases between states in which the court produces binding rulings between states that agree, or have previously agreed, to submit to the ruling of the court; and advisory opinions, which provide reasoned, but non-binding, rulings on properly submitted questions of international law, usually at the request of the United Nations General Assembly. Advisory opinions do not have to concern particular controversies between states, though they often do. Contentious cases The key principle is that the Court only has jurisdiction on the basis of consent. The court has no true compulsory jurisdiction. Jurisdiction is often a key question for the Court, because it is challenged by the respondent. At the Preliminary Objections phase, a respondent may challenge (i) jurisdiction and/or (ii) admissibility of the case. Article 36 outlines four bases on which the Court's jurisdiction may be founded. Only states may be parties in contentious cases before the ICJ. Individuals, corporations, parts of a federal state, NGOs, UN organs and self-determination groups are excluded from direct participation in cases, although the Court may receive information from public international organisations. This does not preclude non-state interests from being the subject of proceedings if one state brings the case against another. For example, a state may, in case of "diplomatic protection", bring a case on behalf of one of its nationals or corporations. Special agreement First, 36(1) provides that parties may refer cases to the Court (jurisdiction founded on "special agreement" or compromis). This method is based on explicit consent and is, perhaps, the most effective basis for the Court's jurisdiction. It is effective because the parties concerned have a desire for the Court to resolve the dispute, and are thus more likely to comply with the Court's judgment. Parties will usually define the nature of the dispute between them and the legal questions on which they wish the Court to rule. Compromissory clause Second, 36(1) also gives the Court jurisdiction over "matters specifically provided for ... in treaties and conventions in force". Many treaties will contain a compromissory clause, providing for dispute resolution by the ICJ. For instance, Article 36(2) of the United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances provides for mediation and other dispute-resolution options, but also states that "[a]ny such dispute which cannot be settled ... shall be referred, at the request