Rennesøy is a former municipality in Rogaland county, Norway. It was merged into Stavanger municipality on 1 January 2020. It was located in the traditional district of Ryfylke. The administrative centre of the municipality is the village of Vikevåg. Other villages in Rennesøy included Askje and Sørbø. The municipality encompassed a number of islands on the south side of the Boknafjorden, north of the city of Stavanger.

At the time of its dissolution, the 66-square-kilometre (25 sq mi) municipality was the 404th largest by area out of the 422 municipalities in Norway. Rennesøy was the 207th most populous municipality in Norway with a population of 4,892. The municipality's population density is 75.4 inhabitants per square kilometre (195/sq mi) and its population has increased by 38.7% over the last decade.

The parish of Rennesø was established as a municipality on 1 January 1838 (see formannskapsdistrikt law). On 1 July 1884, the municipality was split in two with the islands of Mosterøy, Klosterøy, Fjøløy, Kvitsøy, and the western part of Åmøy forming the new municipality of Mosterøy, and the islands of Rennesøy and Brimse remained as Rennesøy municipality. This split left Rennesøy with 1,092 residents, less than half of its previous population. The island of Kvitsøy later became an independent municipality of its own.

On 1 July 1918, the Hanasand area of the neighboring municipality of Finnøy (population: 72) that was located on the island of Rennesøy was transferred to Rennesøy municipality.

During the 1960s, there were many municipal mergers across Norway due to the work of the Schei Committee. On 1 January 1965, the municipality of Mosterøy was merged back into Rennesøy. Prior to the merger, Rennesøy had 1,370 residents.

On 1 January 2020, the municipalities of Finnøy, Rennesøy, and Stavanger were merge into one, large municipality called Stavanger.

The municipality (originally the parish) is named after the main island of the municipality, Rennesøy (Old Norse: Rennisøy). The meaning of the first element is unknown. One possibility is that it comes from the word rani which means "snout", likely referring to the shape of the mountain Hodnafjellet on the southeast part of the island. The last element is øy which means "island". Historically, the name of the municipality was spelled Rennesø. On 3 November 1917, a royal resolution changed the spelling of the name of the municipality to Rennesøy. The letter y was added to the end of the word to "Norwegianize" the name (ø is the Danish word for "island" and øy is the Norwegian word).

The coat of arms was granted on 20 February 1981. The official blazon is "Azure, two crosiers addorsed argent" (Norwegian: I blått to oppveksande adosserte sølv krumstavar). This means the arms have a blue field (background) and the charge is a set of two crosiers standing vertically and mirroring each other. The charge has a tincture of argent which means it is commonly colored white, but if it is made out of metal, then silver is used. The blue represents the ocean, an important feature for this island municipality. The crosiers represent the importance of Norway's oldest and best preserved monasteries, Utstein Abbey, located in the municipality. It was originally an Augustinian monastery, its abbot having a crozier as its symbol. Since Basel, Switzerland already had a crozier on its coat of arms, Rennesøy chose a design with two of them so that it would be different. The arms were designed by Svein Magnus Håvarstein. The municipal flag has the same design as the coat of arms.

The Church of Norway had two parishes (sokn) within the municipality of Rennesøy. It was part of the Tungenes prosti (deanery) in the Diocese of Stavanger.

Churches in Rennesøy

Parish (sokn)	Church name	Location of the church	Year built
Mosterøy	Askje Church	Askje, Mosterøy island	1846
	Utstein Church	Klosterøy island	1280
	Vestre Åmøy Chapel	Åmøy island (western side)	1953
Rennesøy	Hausken Church	Vikevåg, Rennesøy island	1857
	Sørbø Church	Sørbø, Rennesøy island	1130

The island municipality sat on the south side of the large Boknafjorden. It consists of about 80 islands, most of which are uninhabited. The main islands are Rennesøy, Mosterøy, Klosterøy, Fjøløy, Sokn, Bru, Brimse, and the western part of Åmøy (the eastern part is part of Stavanger municipality). All of the main islands are connected together and to the mainland by a series of bridges and tunnels (except for Brimse which has a ferry connection). The Fjøløy Lighthouse is located in the northwestern part of the municipality, lighting a main shipping channel to Stavanger.

Historical population
Year	1865	1875	1891	1900	1910	1920	1930	1946	1951	1960	1970	1980	1990	2000	2010	2019
Pop.	2,453	2,477	1,086	1,110	1,003	1,116	1,260	1,485	1,483	1,438	2,079	2,299	2,561	3,111	4,035	4,847
±% p.a.	—	+0.10%	−5.02%	+0.24%	−1.01%	+1.07%	+1.22%	+1.03%	−0.03%	−0.34%	+3.76%	+1.01%	+1.09%	+1.96%	+2.63%	+2.06%
Note: The municipal borders were changed in 1884 and 1965, causing a significant change in the population. Source: Statistics Norway and Norwegian Historical Data Centre

While it existed, this municipality was responsible for primary education (through 10th grade), outpatient health services, senior citizen services, unemployment, social services, zoning, economic development, and municipal roads. During its existence, this municipality was governed by a municipal council of directly elected representatives. The mayor was indirectly elected by a vote of the municipal council. The municipality was under the jurisdiction of the Stavanger District Court and the Gulating Court of Appeal.

The municipal council (Kommunestyre) of Rennesøy was made up of 21 representatives that were elected to four year terms. The party breakdown of the final municipal council was as follows:

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

• 1892-1913: Jacob Kristensen Austbø
• 1999-2007: Jostein Eiane (KrF)
• 2007-2011: Ommund Vareberg (H)
• 2011-2019: Dagny Sunnanå Hausken (Sp)

Since 1992, Rennesøy municipality has been connected to the mainland by a series of bridges and undersea tunnels. The Byfjord Tunnel connects the mainland to the island of Sokn, and it is part of the European route E39 highway. The island of Sokn is connected to the three islands of Åmøy, Bru, and Mosterøy by bridges. Mosterøy is connected to Fjøløy and Klosterøy by short bridges and to Rennesøy by the undersea Mastrafjord Tunnel. Rennesøy island is also connected to the island of Vestre Bokn (across the Boknafjorden) by ferry. Furthermore, the island of Rennesøy is connected to the two islands of Finnøy and Talgje in the neighboring municipality of Finnøy to the northeast by the Finnøy Tunnel.

• Media related to Rennesøy (former municipality) at Wikimedia Commons
• The dictionary definition of Rennesøy at Wiktionary
• Rogaland travel guide from Wikivoyage