The UN inspectors have been looking for any weapons of mass destruction using hi-tech equipment.
It's the first time Iraq's leader - Saddam Hussein - has let them in for four years.
If the inspectors find something it could mean Britain and America go to war with Iraq.
And if anyone's found to be hiding weapons it could mean the same thing.
They've got till the end of January to search the country.
Saddam has until 8 December to hand over a list of his weapons which will be compared to what the inspectors find.