No one knows exactly what their mission is, but driving the Taleban from Kandahar, the only major city they still control, is likely.
Kandahar is used by the Taleban as their capital city, and because of this it is expected to be very heavily protected.
Trying to catch al-Qaeda
They may also be trying to find members of the al-Qaeda terrorist group controlled by Osama Bin Laden, the man suspected of organising the terrorist attacks in September.
Hundreds of troops have already landed, travelling in helicopters at night, and lots more are expected to join them soon from nearby American ships.