Romerike is a traditional district located east of Oslo in southeastern Norway. It encompasses the majority of Akershus County in the region of Eastern Norway (Østlandet). Romerike is further sub-divided into Upper Romerike (Øvre Romerike) in the north and Lower Romerike (Nedre Romerike) in the south. Upper Romerike consists of the municipalities of Hurdal, Eidsvoll, Nannestad, Ullensaker, Nes, and usually Gjerdrum, which is sometimes considered part of Lower Romerike. Lower Romerike is typically defined as consisting of Nittedal, Lillestrøm, Lørenskog, Rælingen, and Aurskog-Høland. Former Rømskog municipality was not part of Romerike but was merged into Aurskog-Høland; Enebakk municipality is the borderland between Lower Romerike and Follo district, but is usually considered part of the latter.
The name of Romerike means "Realm of the Raumar/Reamas tribe". Romerike was a petty kingdom prior to the unification of Norway. The Raumar/Reamas tribe in turn derived their name from the Rauma river, an old name for the lower part of Glomma. The name "Rauma" likely etymologically means "noisy" or "thundering", referring either to the river's waterfalls in general, or specifically to the confluence of Glomma and Vorma near Årnes town.