US Marine Corps General Joseph Dunford took over as commander of NATO forces in Afghanistan at a ceremony at the alliance's headquarters outside Kabul on Sunday.
General Dunford will be responsible for overseeing the withdrawal from Afghanistan of most American troops as the United States brings its longest war to an end.
The war is in its 11th year and the Afghan military now leads major operations.
Most foreign troops are due to be gone by the end of the year.
"Today is not about change, it's about continuity," General Dunford said. "What has not changed is the will of this coalition."
His predecessor, General John Allen, who is to become NATO supreme commander based in Europe, said: "We will be victorious."
Afghan defence minister Bismillah Khan said there had been great progress during General Allen's tenure.