The municipality encompassed a number of islands on the south side of the Boknafjorden, north of the city of Stavanger.

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 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 crosiers represent the importance of Norway's oldest and best preserved monasteries, Utstein Abbey, located in the municipality.

The Fjøløy Lighthouse is located in the northwestern part of the municipality, lighting a main shipping channel to Stavanger.

The municipal council (Kommunestyre) of Rennesøy was made up of 21 representatives that were elected to four year terms.

The Byfjord Tunnel connects the mainland to the island of Sokn, and it is part of the European route E39 highway.

Mosterøy is connected to Fjøløy and Klosterøy by short bridges and to Rennesøy by the undersea Mastrafjord Tunnel.