Nidaros, Niðarós or Niðaróss was the medieval name of Trondheim in Norway, when it was the capital of the country's first Christian kings. It was named for its position at the mouth (Old Norse: óss) of the River Nid (today's Nidelva).

Although the capital was later moved to Oslo, Nidaros remained the centre of Norway's spiritual life until the Protestant Reformation. The archdiocese of Nidaros was separated from Lund in Scania by the papal legate Nicholas Breakspeare in 1152 and the shrine of Saint Olaf in Nidaros Cathedral was Northern Europe's most important pilgrimage site during the Middle Ages. Archbishop Olav Engelbrektsson served as a leader of Norway in attempting to resist the Danish Reformation but was forced into exile by King Christian III in 1537. The archdiocese was abolished and replaced with a Lutheran superintendenture.

Pre-Reformation

The Christianization of Norway was begun by Haakon the Good (d. 961), and carried on by Olaf Trygvesson (d. 1000) and Saint Olaf Haraldsson (d. 1030), two Vikings who had converted and been baptized at Andover in England and at Rouen in Normandy respectively.

Nidaros was a Norwegian newspaper, published in Trondheim in Sør-Trøndelag.

Nidaros was started on 1 May 1902. Its first editor was former Dagsposten editor Håkon Løken, and with its Liberal Party affiliation Nidaros became the largest newspaper in Trondheim, with a circulation of 20–30,000. Among the political disputes of the time were electrification of the city's tramway system, establishment of a technical institution in Trondheim, the Norwegian Institute of Technology, and the eventual Dissolution of the union between Norway and Sweden. Løken left in 1909. From 1910 to 1911 Atle Øgaard was editor, and Kr. Aug. Retvedt took over from 1911 to 1917. Hjørvard Torsvik edited the newspaper from 1917 to 1930. Olav Røgeberg was chief editor from 1930 to 1937, and Fr. Lützow Holm edited Nidaros from 1937 to 1941. A great success was the feuilleton Bør Børson, Johan Falkberget's satirical story from the boom period during World War I, which was printed in the newspaper before being released as a book. The newspaper became less popular during and after the city naming controversy, when the name of the city Trondhjem was changed to Nidaros, and then among popular protest changed a second time to Trondheim. The anti-Nidaros activists did not like that the newspaper Nidaros retained its name.