The ICC is an independent international organization, with international legal personality, with its headquarters in The Hague, Netherlands.
It was created by treaty: on 17 July 1998, 120 States adopted the Rome Statute & it entered into force (following ratification by 60 states) on 1 July 2002. Details of states parties can be found online.
Under Article 5 of the Rome Statute, the ICC's core jurisdiction encompasses the "most serious crimes of concern to the international community as a whole" categorised as genocide, crimes against humanity, war crimes and aggression.
The ICC is not part of the UN but there is cooperation between the two at many levels, and the Rome Statute (eg Arts 13(b) and 16) accords the UN certain powers in certain circumstances.
The Court reached its first verdict on 14 March 2012