The Namsos Line (Norwegian: Namsosbanen) is a 51-kilometer-long (32 mi) railway line between the village of Medjå and the town of Namsos in Trøndelag county, Norway. The line branches off from the Nordland Line at Grong Station and runs through Grong Municipality, Overhalla Municipality, and Namsos Municipality. The line largely follows the river Namsen (and it crosses the river twice). The section from Grong to Skogmo is maintained, although not used for ordinary traffic. The section from Skogmo to Namsos is closed, but the infrastructure remains.

Planning of the line started in the 1870s and it was originally thought as part of the Nordland Line. This resulted in a debate of whether the Nordland Line should run from Steinkjer via Beitstad and Namsos to Grong (the Beitstad Line) or via Snåsa to Grong, with a branch to Namsos. The latter was selected as it gave the shortest route for the Nordland Line, but gave a longer distance southwards from Namsos and went through a less densely populated area. The line was passed by Parliament in 1913, although construction did not start until 1921. In 1927, construction was halted, but resumed the following year, although the line was built with substandard permanent way. In November 1933 traffic started, and Namsos became the northernmost port in Norway with railway connection to southern Norway, until 1940 when the Nordland Line reached Mosjøen. Passenger traffic was terminated in 1977, and the line has been closed for ordinary traffic since 2002.

The Namsos Line branches from the Nordland Line at Grong and runs 50.60 kilometers (31.44 mi) to Namsos. Prior to 1981, the line had a different terminus in Namsos and was 51.61 kilometers (32.07 mi) long. The curve radius is 250 meters (820 ft) and the maximum gradient is 1.25 percent. The line has five tunnels, with a combined length of 338 meters (1,109 ft). The line is standard gauge, non-electrified, lacks centralized traffic control, automatic train control, and train radio. The railway line is owned and maintained by the Norwegian National Rail Administration. The section from Grong to Skogmo, Overhalla, remains open and maintained, but is not used for ordinary traffic. The section from Skogmo to Namsos remains, but is not maintained.

After Grong Station, which is located 219.54 kilometers (136.42 mi) from Trondheim Central Station and 50.9 meters (167 ft) above mean sea level (AMSL), the line runs over Tømmeråsfoss on the 45-meter-long (148 ft) Sanddøla Bridge and then over the 107-meter-long (351 ft) Røttesdal Vidaduct. The line then runs past Dun Station (3.31 km or 2.06 mi from Grong Station), before Sjemsvoll Station (6.30 km or 3.91 mi) and Jørem Station (9.37 km or 5.82 mi). Next the line reaches Øyheim Station (11.99 km or 7.45 mi), which has a passing loop. The line then passes into Overhalla and continues to Øysletta Station (11.99 km or 7.45 mi), before crossing to the north shore Namsen on the 195-meter-long (640 ft) Bertnem Bridge.

It passes Heknbakk Station (19.08 km or 11.86 mi) before Skogmo, where there is an industrial spur. This is the end of the part of the line which remains open to traffic. The line then reaches Skogmo Station (22.22 km or 13.81 mi), which has a passing loop. It then crosses Namsen on the 89-meter-long (292 ft) Bjøra Bridge and reaches Himo Station (44.92 km or 27.91 mi). The line then reaches Overhalla Station (25.58 km or 15.89 mi), which has a passing loop and serves the municipal center of Ranemsletta.

The line continues on a 54-meter-long (177 ft) bridge over Reina before reaching Barlia Station (27.07 km or 16.82 mi), Øysvoll Station (29.88 km or 18.57 mi), Myrmo Station (32.44 km or 20.16 mi) and Halvardsmo Station (35.11 km or 21.82 mi). An industrial spur then branches off before the main line reaches Skage Station (36.90 km or 22.93 mi), which has a passing loop. The line crosses a 56-meter-long (184 ft) bridge over Myrelven before passing through the 150-meter-long (490 ft) Bergeng Tunnel and the 29-meter-long (95 ft) Brudalsøy Tunnel.

Next the line reaches Grytøya Station (40.55 km or 25.20 mi) before running through the 46-meter-long (151 ft) Vika Tunnel. It continues past Kvatninga Station (43.41 km or 26.97 mi) and then over Moeosen on a 45-meter-long (148 ft) bridge. Next it reaches Meosen Station (44.47 km or 27.63 mi), Høyknes Station (48.02 km or 29.84 mi) and Angelskjæret Station (50.13 km or 31.15 mi). The line then runs through the 69-meter-long (226 ft) Hønhaugen I Tunnel and the 84-meter-long (276 ft) Hønhaugen II Tunnel. Originally the line went to the old Namsos Station (50.60 km or 31.44 mi from Grong and 2.8 meters (9 ft 2 in) AMSL), but since 1981, the line has been shortened to terminate at the new Namsos Station (51.61 km or 32.07 mi).

Because the line was built during the Great Depression and NSB was experiencing an operating loss for the first time in its history, minimal investments were made in stations and their facilities. The main architects were Gerhard Fischer and Bjarne F. Baastad, who both worked for the in-house NSB Arkitektkontor. The line's architecture is designed in Neoclassisism, and is, along with the Ålgård Line, the only line which employed this style consistently. Neoclassical architecture on other lines were only used for individual buildings.