Øyer is a municipality in Oppland county, Norway. It is part of the traditional region of Gudbrandsdal. The administrative centre of the municipality is the village of Tingberg.The parish of Øier was established as a municipality on 1 January 1838 (see formannskapsdistrikt). It is one of very few municipalities in Norway with unchanged borders since that date.
The Old Norse form of the name was Øyja (accusative case and dative case) which comes from the word Øyi (nominative case). Two lakes in Norway had the name Øyi(r) in Norse times (now called Øymark and Øyeren), and these names are derived from the word øy which means "flat and fertile land along the edge of the water". This name is probably given to this area because the Lågen river widens out in the central part of the municipality and creates two river-lakes (called the Jemnefjorden and Gildbusfjorden). Øyi was probably the old name of one (or both) of these "fjords". Prior to 1918, the name was spelled "Øier".