Statute of the International Court of Justice

The Statute of the International Court of Justice is an integral part of the United Nations Charter, as specified by Chapter XIV of the United Nations Charter, which established the International Court of Justice. The statute's chapters are:

Under Article 38.2, the court is allowed to decide a case ex aequo et bono if the parties agree thereto.

All 193 UN member states are parties to the Statute by virtue of their ratification of the UN Charter. Under Article 93(2) of the UN Charter, states which are not a member of the UN may become a party to the Statute, subject to the recommendation of the UNSC and approval of the UNGA. As of 2015, neither of the UN observer states, the State of Palestine and the Vatican City, nor any other state are parties to the statute under these provisions. Switzerland (1948-2002), Liechtenstein (1950-1990), San Marino (1954-1992), Japan (1954-1956), and Nauru (1988-1999) were all parties to the Statute prior to becoming UN member states.

...
Wikipedia