Rennesøy is a municipality in Rogaland county, Norway. It is part of the region of Ryfylke. The administrative center is the village of Vikevåg.The parish of Rennesø was established as a municipality on 1 January 1838 (see formannskapsdistrikt). Mosterøy was separated from Rennesøy on 1 July 1884. It was, however, merged back with Rennesøy on 1 January 1965 (but without Kvitsøy).The Old Norse form of the name was Rennisøy. The meaning of the first element is unknown and the last element is øy which means "island". Before 1918, the name was written "Rennesø".