(Nåavmesjenjaelmie ) is a municipality in Trøndelag county, Norway. It is part of the Namdalen region. The administrative centre of the municipality is the town of Namsos. Some of the villages in the municipality include Bangsund, Klinga, Ramsvika, Skomsvoll, Spillum, Sævik, Dun, Salsnes, Nufsfjord, Lund, Namdalseid, Sjøåsen, Statland, Tøttdalen, and Sverkmoen.
The municipality is the 30th largest by area out of the 356 municipalities in Norway. Namsos is the 80th most populous municipality in Norway with a population of 15,001. The municipality's population density is and its population has decreased by 2.1% over the previous 10-year period.
The municipality is named after the town of Namsos which was established in 1846. The town was named after its location at the mouth of a river. The first element is Nams- which comes from the name of the river Namsen and the last element is os which means the "mouth of a river". The river name has an uncertain origin. The first part of the river name comes from the Old Norse word Nauma) which has an unknown meaning, but it may come from the word naust which means "boat". The second part of the river name -sen (sær) which means "sea". In 2019, the municipality was formally given a co-equal name in the Southern Sámi language: Nåavmesjenjaelmien tjïelte.
The coat of arms was granted to the town of Namsos on 5 May 1961. They were re-granted on 21 October 1966 when the town was merged with neighboring areas to create a new, larger Namsos Municipality. The official blazon is "Gules, a moose head couped Or" (På rød bunn et gull elghode). This means the arms have a red field (background) and the charge is a moose head. The moose head has a tincture of Or which means it is commonly colored yellow, but if it is made out of metal, then gold is used. The moose was chosen as a symbol for the municipality, since Namsos is the capital of the forest-rich Namdalen region, and the moose is the "king of the forest". The arms were designed by Hallvard Trætteberg. The municipal flag has the same design as the coat of arms.