Asker municipality is a municipality in Viken county and Akershus constituency, established on 1 January 2020. The municipality consists of the settlements Asker, Røyken and Hurum, which until 2020 were independent municipalities. The entire merged municipality is located within the Oslo region. The joint political committee that led the merger referred to the new municipality «New Asker municipality». The merged municipality has also been referred to as "Stor-Asker".

Before 2020, Asker was located in Akershus county and makes up the northern quarter of the new municipality, while Røyken and Hurum were located in Buskerud and make up the southern three quarters. The southern part of Asker municipality consists of the peninsula and the landscape Hurumlandet. The entire merged municipality lies within what until 1919 was Akershus diocese. Asker municipality is located in the diocese of Oslo, Oslo team parish and Oslo police district.


In Asker, the landscape consists largely of forest, at the same time as the closer coast towards the Inner Oslo Fjord in the northeast and towards the Drammensfjord in the southwest turns into a plain landscape and areas with cultivated land in the valley stretches. The geology of the landscape is also varied and bears clear traces of the ice ages.

Farthest northwest in the municipality is Vestmarka, which is located on a plateau at 300-400 masl. On the southern edge of this plateau is a ridge with a number of peaks, with Bergsåsen (459 meters above sea level) and Furuåsen (approx. 458 meters above sea level) being Asker's highest points. In the extension of this ridge, to the northeast, lies Skaugumsåsen (349 meters above sea level).

On the opposite side of Asker center from Skaugumsåsen is Vardåsen, which is quite exactly the same height. These two peaks tower over the lower landscape along the west side of the Inner Oslo Fjord. South of Vardåsen is Askerbørskogen, which is an east-going hanging valley that empties into the hillside above Heggedal. Between Askerbørskogen and Røyken is Kjekstadmarka, with Brennåsen (361 meters above sea level) as the highest point. South of Røyken is Villingstadmarka, with Villingstadåsen (357 meters above sea level) as the highest point.

Hurumlandet is the southern part of the municipality. The east side of Hurumlandet has a large higher-lying outfield area, Hurummarka, which is located at around 200-300 masl. Hurumlandet's highest point is Stikkvannskollen (361 meters above sea level). In the southwestern part of Hurumlandet are lower-lying agricultural areas, with hills in between. The southernmost of these hills is Haraldsfjellet (208 meters above sea level).

Asker's coastline is 196.8 km, of which 124.3 km runs along the mainland and 72.5 km along islands. The coastline along the mainland is divided into three approximately equal parts towards the Inner Oslofjord, the Outer Oslofjord and the Drammensfjord. It starts at the border with Bærum in the northeast, and extends around Hurumlandet to the border with Lier. Most of the islands are located in the Inner Oslo Fjord, several of which are inhabited: