Gudbrandsdalen is a valley and traditional district in the Norwegian county of Oppland. The valley is oriented in a north-westerly direction from Lillehammer and the lake of Mjøsa, extending 230 kilometers (140 mi) toward Romsdalen. The river of Gudbrandsdalslågen flows through the valley, starting from Lesjaskogsvatnet and ending at Mjøsa.
The valley is divided into three parts: Norddalen (the municipalities of Lesja, Dovre, Skjåk, Lom, Vågå and Sel), Midtdalen (the municipalities of Nord-Fron, Sør-Fron and Ringebu), and Sørdalen (the municipalities of Øyer, Gausdal and Lillehammer).
 The name
The name Gudbrandsdalen means 'the valley/dale of Gudbrand'. Gudbrand (Norse Guðbrandr) is an old male name compounded of guð, 'god' and brandr, 'sword'. This was probably a title used by the kings of the valley living at Hundorp.
Gudbrandsdalen was shaped by the recent ice age and rivers from the present glacial areas in Jotunheimen and Dovre. Bones and teeth from mammoths and musk oxen, living in the area at that time, are found in the valley.
1015 - Gudbrandsdalen is mentioned extensively in the Heimskringla (Chronicle of the Kings of Norway) by Snorri Sturluson. The account of King Olaf's (A.D. 1015-1021) conversion of Dale-Gudbrand to Christianity is popularly recognized.
1349 to 1350 – The Black Plague halved the population in Gudbrandsdal. This resulted in a temporary improvement for the lower classes as crofters became scarce and even the poor were able to rent the better farms in the bottom lands.
1537 - During the Reformation the Church was subordinated to the lendmenn or sheriffs. Church property was appropriated by the Crown and the King became the biggest Gudbrandsdalen landowner.
1612 - In the Battle of Kringen, near Otta in Gudbrandsdalen, local peasants defeated a Scottish mercenary army. The legends of this battle live on to this day, including the story of how the peasant girl Prillar-Guri lured the Scots into an ambush by playing the traditional ram's horn.
1670 to 1725 – Most of the royal property was sold off to pay for war debts, first to established property holders, but increasingly to peasant proprietors. A freeholders' era began and a new "upper class" of land holders was formed.
1789 Storofsa - the greatest flood recorded in Gudbrandsdalen: Several farms were devastated, and many people killed.
1827 the city of Lillehammer is established.
1904 The outdoor museum of Maihaugen, exhibiting old houses from all parts of Gudbrandsdalen, opened at Lillehammer.
 Mountain areas close to the valley
 Named for Gudbrandsdal