The formal transfer of command in 14 provinces in the east to Nato’s International Security Assistance Force (Isaf) took place on Thursday at a ceremony at its headquarters in Kabul.
The ceremony was attended by Hamid Karzai, the Afghan president, and the senior commanders of both forces.
General David Richards, the Isaf commander, praised the work of the US-led forces and told the gathering that his force was committed to continuing the work and "helping Afghanistan on its journey towards a more secure future".
The US, with 13,250 troops, will remain the biggest troop-contributor in the 33,000-strong Nato force.
“A key point to remember in this transition is that the United States maintains its full commitment to Afghanistan. It will be undiminished,” Lieutenant-General Karl Eikenberry, the coalition commander, said.
“As a Nato member, the United States will remain by far the single-largest contributor of troops and military capability.”
“As a Nato member, the United States will remain by far the single-largest contributor of troops and military capability”
Lieutenant-General Karl Eikenberry, the coalition commander
Of the 41,000 foreign troops in Afghanistan, only 8,000 US troops will function outside Nato control - those tracking al-Qaeda terrorists or involved in air operations.
The command consolidation confines direct US control to a single main enclave, the large American base at Bagram.
A US Army helicopter unit based at Kandahar airfield and the US-operated prisons and interrogation centres at Bagram will also remain under the US command.
Nato will continue to transfer its detainees to Afghan police.
The 37-nation Isaf took over command of the Taliban-dominated southern provinces from the US-led forces on July 31, moving into one of the most hostile areas of the country.
The east also contains several strongholds of the Taliban and some military forces say al-Qaeda also has a presence there.
The coalition invaded Afghanistan in October 7, 2001 - and within weeks toppled the Taliban government which had sheltered al-Qaeda leaders blamed for the September 11 attacks in the United States.
But the Taliban has regrouped and its renewed insurgency is going through its bloodiest phase yet.