The Rome Statute of the International Criminal Court (or Rome Statute) is the treaty which established the International Criminal Court (ICC). It entered into force in 2002. Since it is a treaty that establishes an international court, it is called a Statute (note this is a different usage of the word "statute" from that commonly used in law.)
The Statute provides for the ICC to have jurisdiction over three main classes of offences: genocide, crimes against humanity and war crimes. The treaty establishing the court gives a specific definition of genocide in Article 6, a list of crimes against humanity in Article 7, a lengthy and detailed list of war crimes in Article 8. The Statute also provides for the court to have jurisdiction over the crime of aggression, but only once a definition for that crime has been adopted by an amendment to the Statute. (source) (http://www.un.org/law/icc/statute/99_corr/2.htm)
Only 7 nations (China, Iraq, Israel, Libya, Qatar, the United States and Yemen) voted against the Rome Statute of the International Criminal Court in 1998. Israel, the United States and Yemen signed the statute at the end of 2000, but the United States has continued to insist on immunity for American forces.
On May 6, 2002, the United States informed the United Nations Secretary-General that "the United States does not intend to become a party to the treaty. Accordingly, the United States has no legal obligations arising from its signature on December 31, 2000." This was widely described as "unsigning" the treaty or "withdrawing" the United States' signature, although the United States in its letter did not use that terminology, and the United Nations has not removed the name of the United States from the official list of signatories.