They filled vacancies left by three judges following their separate resignations.
Those sworn in are: Frenchman Bruno Cotte, Japanese Fumiko Saiga and Ugandan Daniel David Ntanda Nsereko.
They were elected by the Assembly of States Parties to the Rome Statute of the ICC at UN headquarters in New York.
These judges will fill vacancies left by Judges Maureen Harding Clark (Ireland), Karl T. Hudson-Phillips (Trinidad and Tobago), and Claude Jorda (France).
One of the first crucial assignment of the judges will be election of a new Registrar to replace Frenchman Bruno Cathala, who declined a second mandate after serving the court for five years.
The registrar will be elected by a secret ballot.
Ten candidates were originally lined up last October, among which included the current Registrar of the International Criminal Tribunal for Rwanda (ICTR), Senegalese Adama Dieng, and the Chief of Prosecution, Italian Sylvana Arbia.
Dieng has been nominated by the African Union to contest the post.
Close to a hundred candidates had been selected initially for the post which was pruned to ten and finally three, which also includes Dieng.
The President of the Assembly of States Parties, Bruno Stagno Ugarte, said that "the ICC is a permanent headlight and a glimmer of hope for the victims of crimes against humanity,".
The ICC Prosecutor has so far opened four investigations in the alleged crimes against humanity committed by rebels or evil forces.
These are in Uganda, the Democratic Republic of Congo (DRC), Darfur and the Central African Republic. The Court has issued ten arrest warrants, most of which are under seal.
No trial has been opened but two men are held by the Court-- Congolese militiamen Thomas Lubanga and Germain Katanga.
The ICC budget for 2008 is approximately 130 million US dollars.
© Agence Hirondelle