Gjerstad is a municipality in Agder county, Norway. It is located in the traditional region of Sørlandet, in the southeastern part of the county, along the border with Telemark county. The administrative centre of the municipality is the village of Gjerstad. Other villages in the municipality include Ausland, Eikeland, Fiane, Gryting, Østerholt, Rød, Sundebru, and Vestøl.

The 322-square-kilometre (124 sq mi) municipality is the 256th largest by area out of the 356 municipalities in Norway. Gjerstad is the 260th most populous municipality in Norway with a population of 2,421. The municipality's population density is 7.9 inhabitants per square kilometre (20/sq mi) and its population has decreased by 2.5% over the previous 10-year period.

The parish of Gjerstad was established as a municipality on 1 January 1838 (see formannskapsdistrikt law). The borders have not changed since that time.

The municipality (originally the parish) is named after the old Gjerstad farm (Old Norse: Geirreksstaðir) since the first Gjerstad Church was built there. The meaning of the first element is uncertain. One possibility is that it is the genitive case of the male name Geirrekr. Another possibility is that it comes from the word geirr which means "spear". The last element of the name is the plural form of staðr which means "place", "abode", or "town". Historically, the name of the parish was spelled Gerikstadum (c. 1400), Gierestat (c. 1567), Gierrestad, and Gjerrestad.

The coat of arms was granted on 18 April 1986. The official blazon is "Gules, three knives argent in fess palewise points to the base" (Norwegian: På raud grunn tre opprette sølv knivar). This means the arms have a red field (background) and the charge is three knives pointing downwards. The knives have a tincture of argent which means it is commonly colored white, but if it is made out of metal, then silver is used. The knife was chosen as a symbol for the smithies and knife makers in the municipality. Knife making has long been a local tradition for which Gjerstad is well known. The arms were designed by Odd Kjell Mostad. The municipal flag has the same design as the coat of arms.

The Church of Norway has one parish (sokn) within the municipality of Gjerstad. It is part of the Aust-Nedenes prosti (deanery) in the Diocese of Agder og Telemark.

Churches in Gjerstad

Parish (sokn)	Church name	Location of the church	Year built
Gjerstad	Gjerstad Church	Gjerstad	1848

Until about 1650, the prestegjeld of Gjerstad (the precursor to today's municipality) was named Vissedal (from vidr-ser-dalr meaning "wood-sea-dale"), a very proper description of the area. Gjerstad has been inhabited from the Stone Age and Viking Age through modern times. Agriculture has long been important, and until only decades ago the more marginal outfields in Upper Gjerstad were still utilized. Forestry also provided an important historic economic contribution, and logs were driven on rivers and streams in the municipality. To aid log transport by floating, numerous dams were constructed. Eikeland Ironworks were a significant contribution to the economy as well.

Gjerstad municipality has numerous glacially formed features, including a U-shaped valley, tarns, and lakes, most notably the large lake Gjerstadvatnet. It located in Agder county and it is bordered to the north by Nissedal and Drangedal municipalities (both in Telemark county); to the east by Kragerø municipality (also in Telemark); to the south by Risør municipality; and to the southwest by Vegårshei municipality. There are several larger roads that traverse Gjerstad: European route E18, Norwegian County Road 417, and Norwegian County Road 418.

Gjerstad Municipality is responsible for primary education (through 10th grade), outpatient health services, senior citizen services, welfare and other social services, zoning, economic development, and municipal roads and utilities. The municipality is governed by a municipal council of directly elected representatives. The mayor is indirectly elected by a vote of the municipal council. The municipality is under the jurisdiction of the Agder District Court and the Agder Court of Appeal.

The municipal council (Kommunestyre) of Gjerstad is made up of 17 representatives that are elected to four year terms. The tables below show the current and historical composition of the council by political party.

The mayors (Norwegian: ordfører) of Gjerstad (incomplete list):

• The remains of Eikeland Ironworks can still be seen in the upper valley. Gjerstad was known for its handmade knives and the coat-of-arms recognizes this heritage.
• Horga was a former pagan place of sacrifice which was destroyed by Olav Trygvason, during the introduction of Christianity to Gjerstad. It lies 300 metres (980 ft) from Holmen Gård.
• Holmen Gård in Gjerstad (Norwegian: Holmen Gård i Gjerstad) is the site of a former farm. It was a Norwegian national center for folk art and handicraft until it was sold into private ownership in 2013. The site has been awarded the St. Olaf's Rose (Olavsrosa), a hallmark for Norwegian Heritage which designates especially distinguished places.

• 
  Eikeland verk building
• 
  Road with houses at the Eikeland verk in 1939
• 
  View of the buildings at Holmen Gård
  Credit: ©Torgrim Landsverk
• 
  Main house at Holmen Gård
  Credit: ©Torgrim Landsverk

• Hans Mathias Abel (1738–1803), the priest at Gjerstad Church from 1785 to 1804
• Søren Georg Abel (1772–1820), a politician and also priest at Gjerstad from 1804 to 1821
• Niels Henrik Abel (1802–1829), a distinguished mathematician who spent his boyhood in the rectory at Gjerstad and died young of TB
• Svenum Jensen Vævestad (1849 in Gjerstad – 1898), a farmer and politician
• Morten Ansgar Kveim (1892 in Gjerstad – 1966), a pathologist who described the Kveim test
• Magnhild Hagelia (1904 in Gjerstad – 1996), a politician
• Jan Olav Olsen (born 1950), a politician who was mayor of Gjerstad from 1991 to 1999
• Inger Løite (born 1958 in Gjerstad), a politician
• Knut Magne Valle (born 1974 in Gjerstad), a heavy metal guitarist, songwriter, composer, recording studio owner, record producer, and music arranger
• Torbjørn Urfjell (born 1977), a politician

• Municipal fact sheet from Statistics Norway (in Norwegian)
• Aust-Agder travel guide from Wikivoyage
• Welcome to Holmen Gård in Gjerstad
• Gjerstad.org (in Norwegian)
• Culture in Gjerstad on the map (in Norwegian)