So what's it about, and what happens next?
The ICJ, also known as the World Court, is the highest United Nations legal body.
It should not be confused with the International Criminal Court, also in the Hague, which handles war crimes cases against individuals.
The ICJ deals with disputes between states. That's often about borders but increasingly includes cases by states accusing others of breaking U.N. treaty obligations.
Gambia, for example, brought an ongoing genocide case against Myanmar in 2019 over the latter's treatment of the Rohingya minority group.
South Africa's 84-page filing accuses Israel of committing genocide against Palestinians in Gaza.
It's doing this, South Africa claims, by killing them, causing serious mental and bodily harm, and by creating conditions on life, quote, "calculated to bring about their physical destruction."
South Africa, which has a long history of supporting the Palestinian cause, also alleges that Israel has failed to curb incitement to genocide by its own officials, in violation of the Genocide Convention.
Israel has called the claims baseless and said it will present its case in court.
A government spokesman accused South Africa of an "absurd blood libel."
Israel began its bombardment of Gaza following Hama's October 7 cross-border rampage in which, according to Israeli officials, 1,200 people were killed.
The Israeli military says it tries to avoid harm to civilians but blames Hamas for embedding fighters within residential areas, something the group denies.
Palestinian health officials say the Israeli offensive has so far killed more than 23,000 Palestinians in Gaza.
The ICJ hearing on January 11 and 12 will deal with a request by South Africa for provisional measures including ordering Israel to suspend its military campaign in Gaza.
Such measures are designed to prevent a dispute from getting worse while the court looks at the full case.
The ICJ's rulings are final and without appeal but it has no way of enforcing them.
However, a ruling against Israel could hurt its international reputation and set a legal precedent.
There are several hoops to jump through before a full case could be heard.
The ICJ needs to find that it has prima facie jurisdiction, after which Israel would get another chance to argue the court has no grounds to look at South Africa's claim.
It is not unusual for several years to pass between the initial claim and the actual hearing of the case on its merits.
