Adventdalen (English: Advent Valley) is a 30-kilometre (19 mi) long valley that follows Adventdalselva (Advent Valley River) on the island Spitsbergen in Svalbard, Norway. The valley and the river flow into Adventfjorden and further into Isfjorden.
The end of the valley is at Haugen in Longyearbyen, close to the University Centre in Svalbard. The valley originates from the mountains Slottet and Tronfjellet, under the glaciers Hellefonna and Drønbreen. It runs westwards tovards the Adventfjorden. From northwest, the branch valleys are: Mälardalen, Helvetiadalen, Eskerdalen, Janssondalen, Foxdalen, Bolterdalen, Todalen and Endalen.
On the south side of the valley are several closed mines, and there is a road to these. Mine 7 still is still in operation, 15 kilometres (9.3 mi) from Longyearbyen. The valley has snow scooter trails, and the whole valley has mobile telephone service. At the mouth of the valley was the former location of Svalbard Airport until the current opened in 1975.