Understanding the International Criminal Court (49 pp. pdf).
The court was established by the Rome Statute which dates from 1998 but which entered into force on 1st July 2002. The court has NO jurisdiction for events prior to that date. The court is also a "last resort" and acts where national authorities are not acting to bring alleged perpetrators to justice.
Effect is given in the United Kingdom to the ICC by the International Criminal Court Act 2001
Watching the Law blog 4th September 2012 - Tutu and Blair: The International Criminal Court