The Battle of Hegra Fortress was a 25-day engagement in the 1940 Norwegian campaign which saw a small force of Norwegian volunteers fighting numerically superior German forces from a fortified position. After initial fighting around the Merker Line railway line, the Norwegians pulled back into Hegra Fortress and held off further German attacks before surrendering on 5 May as one of the last Norwegian units active in southern Norway.

The Norwegian campaign (8 April – 10 June 1940) describes the attempt of the Allies to defend northern Norway coupled with Norwegian forces' resistance to the country's invasion by Nazi Germany in World War II.

Planned as Operation Wilfred and Plan R 4, while the German attack was feared but had not happened, HMS Renown set out from Scapa Flow for the Vestfjorden with twelve destroyers on 4 April. British and German naval forces met at the first Battle of Narvik on 9 and 10 April, and the first British forces landed at Åndalsnes on the 13th. The main strategic reason for Germany to invade Norway was to seize the port of Narvik and guarantee the iron ore needed for critical production of steel.The campaign was fought until 10 June 1940 and saw the escape of King Haakon VII and his heir apparent Crown Prince Olav to the United Kingdom.

A British, French and Polish expeditionary force of 38,000 soldiers, many days in, landed in the north. It had moderate success. A rapid strategic retreat took place after Germany's overwhelmingly quick invasion of France in May. The Norwegian government then sought exile in London. The campaign ended with the occupation of the entirety of Norway by Germany, but exiled Norwegian forces escaped and fought on from overseas.