Leader: Jens Stoltenberg
Norway's Jens Stoltenberg took office in October 2014 at a time when NATO's face-off with Russia over Ukraine had sparked tensions not seen since the collapse of the Soviet bloc.
He replaced Anders Fogh Rasmussen, who had been NATO secretary-general since July 2009.
Mr Stoltenberg became Norway's youngest prime minister in 2000, the day after his 41st birthday. He only kept that position briefly, but returned to power in 2005 and stayed on at the head of government until 2013.
He is known for his good relations with Russian President Vladimir Putin. During his decade in power, the two countries signed milestone agreements on the delineation of their frontier in the Barents Sea and on visa exemptions for their border populations.
He is an economist by training and a former leader of the Norwegian Labour Party.
He was unanimously chosen as secretary-general by NATO's policy-making North Atlantic Council.