Hjartdal is a municipality in Telemark county, Norway. It is located in the traditional district of Upper Telemark and Aust-Telemark. The administrative centre of the municipality is the village of Sauland. Other villages in the municipality include Tuddal and Hjartdalsbygda.

The 792-square-kilometre (306 sq mi) municipality is the 146th largest by area out of the 356 municipalities in Norway. Hjartdal is the 299th most populous municipality in Norway with a population of 1,588. The municipality's population density is 2.2 inhabitants per square kilometre (5.7/sq mi) and its population has decreased by 1.3% over the previous 10-year period.

The municipality of Hierdal was established as a municipality on 1 January 1838 (see formannskapsdistrikt). In 1860, the Gransherad area of eastern Hjartdal (population: 1,310) was separated to become part of the new Gransherad Municipality. Also in 1860, the administrative centre of the municipality was moved from Hjartdalsbygda to Sauland. On 23 January 1905, a small, unpopulated area of Hjartdal was transferred to the neighboring Seljord Municipality.

The municipality (originally the parish) is named after the valley name, Hjartdalen (Old Norse: Hjartdalr) since the first Hjartdal Church was built there. The first element is the old name for the local river Hjartdøla. The old river name is likely derived from the word hjǫrtr which means "red deer". The last element is dalr which means "valley" or "dale". Prior to the 20th century, the name was often spelled Hierdal, a corruption of the original name. In the 20th century, the spelling was standardized to Hjartdal, bringing back more of the original spelling.

The coat of arms was granted on 17 February 1989. The official blazon is "Vert, a deer at bay argent" (Norwegian: På grøn grunn ein ståande sølv hjort). This means the arms have a green field (background) and the charge is a red deer (Cervus elaphus) standing at bay. The deer has a tincture of argent which means it is commonly colored white, but if it is made out of metal, then silver is used. They are canting arms because the name of the municipality is derived from the word for deer, a common animal in the rural municipality. The color green was chosen to represent the forests in the area. The arms were designed by Svein G. Carlsen. The municipal flag has the same design as the coat of arms.

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

Up to the 1500s, the Hjartdal parish had been quite large. It stretched from Rauland in the west and Kongsberg to the east. Counting from west to east, the villages of Åmotsdal, Svartdal, Hjartdal, Tuddal, Sauland, Gransherad, Bolkesjø, Jondalen and Lisleherad were all at one point included in the same parish. Sometime after 1687 Lisleherad was transferred to the partish of Heddal. Then in 1860, the Gransherad area was separated. Today, the Hjartdal parish and municipality consists of the three main village areas: Hjartdalsbygda, Sauland, and Tuddal.

Hjartdal 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 Telemark District Court and the Agder Court of Appeal.