Under international law, genocide is defined as committing one or more acts with the intention to destroy, in whole or in part, a national, ethnic, racial or religious group.
There were angry scenes outside the ICJ's building, known as the Peace Palace, as Dutch police struggled to keep groups of Palestinian and Israeli supporters apart.
Red and white police tape has been placed outside the ICJ in an attempt to bring some semblance of order to the chaotic scenes outside.
In Gaza, more than 23,350 people - mostly women and children - have been killed, according to the Hamas-run health ministry, since the war began in the aftermath of Hamas's 7 October attacks on southern Israel. In those attacks some 1,300 people were killed - mainly civilians - and about 240 others taken hostage.
Israeli President Isaac Herzog called the accusations "atrocious and preposterous".
"We will be in the International Court of Justice and we will present proudly our case of using self-defence… under humanitarian law," he said.
Israel's delegation is expected to highlight its right to self-defence under international law - this week, Prime Minister Benjamin Netanyahu said Israel has no intention of permanently displacing the people of Gaza, or occupying the territory.
Unlike the International Criminal Court (ICC), the ICJ cannot prosecute individuals for crimes such as genocide, but its opinions carry weight with the UN and other international institutions.
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