B-52 aircraft, tanks and soldiers on foot are targetting the deep caves of the Tora Bora mountains.
This is where Bin Laden is thought to be hiding - though no one knows where he is for sure.
He may also have fled Afghanistan.
However, Pakistan has placed extra soldiers and helicopter gunships along the 2,500km border to stop him escaping.
New video evidence
Meanwhile, a video linking Bin Laden to the 11 September attacks has been uncovered in a house abandoned by the Taleban.
On it, he says he didn't expect the World Trade Centre to collapse when it was hit by hijacked aircraft.
The US says this proves he knew about the attacks before they happened.