|o Total||19,386 km2 (7,485 sq mi)|
|o Density||2.6/km2 (6.8/sq mi)|
Østerdalen is a valley and traditional district in Innlandet County, in Eastern Norway. It consists of the municipalities Rendalen, Alvdal, Folldal, Tynset, Tolga and Os in the north, Elverum, Stor-Elvdal, Engerdal, Trysil and Åmot in the south. It historically included Särna and Idre, today in Sweden.
Østerdalen is quite wide in most places. Østerdalen is characterized by tranquil landscapes and rounded mountains. The valley is mostly covered by pine forests. Typical of Østerdalen is that large parts of the forest floor are covered with reindeer moss, a variety of lichen.
Glommadal (Glåmdalen) is a designation for the valley formed by the river Glåma (also called the Glomma), which is the longest and largest river in Norway. From Lake Aursund in the north and south to Elverum, the valley is called the Østerdalen. From that point south until Kongsvinger, it is referred to as Solør. As in turns westerly from Kongsvinger until Nes, it is called the Odalen. These designations are also traditional districts, reflecting the designations locals used for their valleys. The upper river valleys of Norwegian rivers have distinctive names which are vestiges of earlier cultural distinctions such as building styles, traditional clothing or bunad and domestic crafts.
The Old Norse form of the name was Øystridalir (Eystridalir) 'the eastern valleys'. The name was referring to the valleys of the rivers Glomma, Rena, Trysilelva and Österdalälven (the parishes Idre and Särna belonged to Norway until 1644). The modern form -dalen is the finite singular of dal m 'dale, valley'.