Halden (pronounced [ˈhɑ̀ɫdn̩] ()), between 1665 and 1928 known as Fredrikshald, is both a town and a municipality in Viken county, Norway. The municipality borders Sarpsborg to the northwest, Rakkestad to the north and Aremark to the east, as well as the Swedish municipalities Strömstad, Tanum and Dals-Ed respectively to the southwest, south and southeast.
The seat of the municipality, Halden is a border town located at the mouth of the Tista river on the Iddefjord, the southernmost border crossing between Norway and Sweden. The town of Halden is located about 120 km (75 mi) south of Oslo, 190 km (120 mi) north of Gothenburg, and 12 km (7.5 mi) east of the border crossing at Svinesund.
Evidence of early human settlements in this region of Norway have been found, particularly in the Svinesund area of the municipality where evidence of early settlements from the Nordic Bronze Age have been found. Named after a small farm Hallen (English: "rise" or "slope") first mentioned in 1629, "Halden", became the city of Fredrikshald in 1665, named after Frederick III of Denmark. The Gud med oss (God be with us) coat-of-arms created in 1665 shows a knight standing on a mountain, yellow on a blue background, and was inspired by the bravery of the citizens of the city in the Dano-Swedish War (1658–1660).
Swedish forces unsuccessfully attempted to invade the town six times between 1658 and 1814. As a reference to the town's citizens burning their own houses to prevent them being taken on 4 July 1716 by the forces of King Charles XII of Sweden, Halden is one of only two cities in Norway's national anthem. In 1718, the Great Northern War ended when Charles XII was shot and killed at the Fredriksten fortress. The fortress had been erected in the 17th century as a replacement for the Bohus Fortress lost at the Treaty of Roskilde in 1658 when Bohuslän was ceded to Sweden. Halden has never been captured by force by any invading army, although it was occupied by Nazi forces in WWII.
In an 1835 census, Fredrikshald was the seventh largest town or city in Norway, with 4,921 inhabitants. In 1838, Fredrikshald became a city municipality (Norwegian: herred), and in 1928, the name was changed back to Halden. Tistedalen, which is 4 kilometres (2 mi) east of Halden, was part of the city from 1686 to 1967, until it was separated from Halden. At the same time, the area of Halden, Tistedalen, and the rural municipalities of Berg and Idd, became the Halden municipality on 1 January 1967.
The political situation in Halden has become infamous in Norway for conflicts between individual politicians and between local political parties. The municipality is governed by the Conservative Party, the Liberal Party, the Christian Democratic Party, the Centre Party, and the Green Party.
The slogan, Halden, IT- og Miljøbyen (Halden, IT and Environment City), is a reference to Halden's relatively large number of information technology companies. In the late 1960s, the most powerful mainframe computer in Norway at the time was located at the Institute for Energy Technology's facilities in Halden. From the 1960s-1980s, Halden was infamous for high levels of industrial pollution, largely originating from the Norske Skog Saugbrugs paper mill (part of Norske Skog since 1989). As a result of projects initiated by both Norske Skog-Saugbrugs and the city authorities, the polluted fjords and rivers of Halden have been cleaned up and the city was dubbed Norway's Environment City in 1996.
One of Norway's two nuclear reactors under decommissioning is located in Halden. The Halden Boiling Water Reactor is a research reactor located 100 metres (328 ft) within Månefjell, adjacent to the Saugbrugs paper mill. The OECD Halden Reactor Project is one of the world's longest running international research collaborations and is the largest international research project in Norway. While the reactor closed in 2018, safety-oriented research collaboration for the nuclear power industry has continued, focusing primarily on human-technology-organisation research. IFE's Man-Technology-Organisation Lab facility in Os Alle was opened by the Prince Regent in 2004 and houses the most recent incarnations of the Halden Man-Machine Laboratory (HAMMLAB) and Halden Virtual Reality Centre's (HVRC) VR laboratory. IFE also has advanced robotics and cybersecurity labs in Halden. The Halden Project at IFE has ensured a steady influx of international guest scientists to the city, many of whom made Halden their permanent homes.
Nexans has a large cable factory in Halden. The main products from this factory are submarine power cables, umbilical cables for subsea installations, and cable systems for heating of subsea pipelines.
Rød Herregård in Halden is one of the best preserved manor houses in Norway. The property features well-preserved buildings, a baroque garden and an English landscape garden. The buildings have their oldest origins of the late 1600s, but were largely built during the last half of the 1700s. The main building contains authentic furnishings including period furniture, hunting trophies, an extensive collection of art and a large weapons collection. 
Rød Herregård was owned and inhabited by members of the Tank and Anker families from 1733 including Carsten Tank and Nils Otto Tank as well as Peter Martin Anker and Nils Anker. The manor house and estate complex was owned by the Tank family through three generations, from 1733 to 1829. Both Danish Crown Prince regent Christian Frederik and Swedish Crown Prince and Regent Charles John were guests at the mansion. The estate was visited by English economist Thomas Robert Malthus during his European tour in 1799.  
In 1961, two foundations were established to maintain the historic property. Rød Manor Foundation (Stiftelsen Rød Herregård) is responsible for the manor house, buildings and gardens. Ankerske Foundation Collections (Stiftelsen De Ankerske Samlinger) is responsible for the contents and the rich archives related to the property.
Halden sights include the Halden Canal system, the two Svinesund bridges, and Høiåsmasten, a partially guyed TV tower. The fortress of Fredriksten has historical museums, and the Østfold University College (Høgskolen i Østfold) is in Halden.
Petroglyphs (rock carvings) dated from the Nordic Bronze Age are found around town, some locally, but more impressive are ones found along Oldtidsveien, the historical road between Halden and Fredrikstad some 20 km (12 mi) north, and around Tanum in Sweden, some 60 km (37 mi) to the south. Jellhaugen, a major tumulus (grave mound) is found west of town.
Halden is surrounded by forests and water, so hiking and fishing locations can easily be found. Deer and elk are a common sight, and wolves have also been observed in the district along the border with Sweden. Raspberries, blackberries, blueberries, wild cranberries, and many varieties of mushroom can be found in the woods in the early autumn. Popular destinations for hikers and other nature lovers include Prestebakke and Kornsjø.
The Gjellestad (Norwegian pronunciation: [ˈjɛ̂lːəˌstɑːd]) ship, also spelt Jellestad, is the remains of a Viking age longship found at the farm of Gjellestad in Halden municipality in Norway in 2018 by the archeologists Lars Gustavsen and Erich Nau. A 2019 examination by the University of Oslo has dated it to earliest AD 733. Originally interred beneath a burial mound, in the present day the ship lies 50 centimetres below the topsoil due to years of plowing.
Due to extensive fungus damage to the hull caused by field drainage, drought and exposure to the air, archaeologists called for an immediate dig to save the ship. Excavation of the ship at Gjellestad began in June 2020, and is led by Christian L. Rødsrud of the Museum of Cultural History. It is estimated to be over 20 metres long, although only parts of the keel have survived. This would mean that the boat is of a similar size to the Gokstad ship. The identity of the boat's occupant has not yet been confirmed, but experts have speculated that it may have belonged to a king or queen.
Outdoor concerts are frequently held at the fortress while the local churches, pubs, and student union are regular venues for indoor concerts. Musicians recorded by the Hitsville and Athletic Sound studios in the Halden region include Motorpsycho, Madrugada, Morten Harket, and Kurt Nilsen. The city's intimate theatre hosts frequent plays by national and local theatre groups, and occasionally serves as a concert hall.
Halden festivals include Tons of Rock (hard rock and metal) in June each year (from 2014 before the festival was moved to Oslo in 2019) and a vegetarian food festival in August. The famous pub "Siste Reis" neighbouring the train station has been voted among the ten best pubs in Europe!
Artists born in Halden that are represented in the Norwegian National Gallery in Oslo include Thomas Fearnley (1802–1842) and Jacob Mathias Calmeyer (1802–1883). Fearnley is locally exhibited at the manor house Rød Herregård. Other significant artists that lived in Halden, but were not born there, include Johannes Fintoe (1786–1870) and Heinrich August Grosch (1763–1843). Grosch's son, Christian Heinrich Grosch (1801–1865), who moved with his parents to Halden at the age of ten, became an influential architect, whose works include seventy-eight churches (including Immanuel Church in Halden), the Bank of Norway, the Oslo Stock Exchange, and the original university buildings in Oslo.
The Halden VBK volleyball club plays in the Premier Division, and while the local ice hockey team Comet did play in the GET-league (Norway's highest ice hockey division) for some years, but they ran into some financial problems in 2008/2009, and is now in division 1. Halden also has many football clubs, the biggest of them, Kvik Halden FK, plays in the Norwegian Second Division. The two handball clubs, Tistedalens TIF in the first division and HK Halden, have teams for children, youth and adults.
One of Norway's few curling centres lies in Halden. Halden Curling Center is host to East-Norway 1 division. In addition there is a separate amateur league with two divisions. Several curlers from Halden have won Norwegian championships and competed internationally.
Halden is one of Norway's highest-security jails. It has acquired a “reputation as the world's most humane prison.” The architectural design of this prison is not like other prisons. The conditions inside the prison have been made as much like life outside the walls as possible. It is in fact to create an environment “as unprisonlike as possible.” This reflects the flagship of the Norwegian justice system, which focuses on rehabilitation rather than punishment. To emplore what makes incarceration in Norway different from being imprisoned in other countries, British journalist Raphael Rowe spent a week at Halden Prison for the Netflix documentary Inside the World's Toughest Prisons (Season 3 Episode 4).