Zemun is a municipality of the city of Belgrade. Zemun was a separate town that was absorbed into Belgrade in 1934. The development of New Belgrade in the late 20th century affected the expansion of the continuous urban area of Belgrade.

According to the 2011 census results, the municipality of Zemun has a population of 168,170 inhabitants.

The Municipality has an area of 153 square kilometres (59 square miles). It is located in the eastern Syrmia region, in the central-western section of the Belgrade City area. The urban section of Zemun is the both most northern and western section of the urban Belgrade. Zemun borders the province of Vojvodina to the west (municipality of Stara Pazova and municipality of Pecinci), and municipalities of Surcin to the south, Novi Beograd to the south-east and Palilula and Stari Grad across the Danube.

The core of the city are the neighborhoods of Donji Grad, Gardoš, Cukovac and Gornji Grad. To the south, Zemun continues into Novi Beograd with which it makes one continuous urban area (neighborhood of Tošin Bunar). In the west it extends into the neighborhoods of Altina and Plavi Horizonti and to the north-west into Galenika, Zemun Polje and further into Batajnica.

Zemun originally developed on three hills, Gardoš, Cukovac and Kalvarija, on the right bank of the Danube, where the widening of the Danube begins and the Great War Island is formed at the mouth of the Sava river. Actually, these hills are not natural features. Zemun loess plateau is the former southern shelf of the ancient, now dried, Pannonian Sea. Modern area of Zemun's Donji Grad was regularly flooded by the Danube and the water would carve canals through the loess. Citizens would then build pathways along those canals and so created the passages, carving the hills out of the plateau. After massive 1876 floods, local authorities began the construction of the stony levee along the Danube's bank. Levee, a kilometer long, was finished in 1889. Today it appears that Zemun is built on several hills, with passages between them turned into modern streets, but the hills are actually manmade.

Loess cliff "Zemun" was protected by the city on 29 November 2013. It consists of the very steep right bank of the Danube and is a typical example of the dry land loess. There are four distinguished loess horizons and four horizons of the fossil earth. The horizons developed during the warmer intervals of the glacials.

The Danube bank in the north is mostly marshy, so the settlements are built further from the river (Batajnica) separated from it by hillocks (up to 114 m). The city of Zemun itself was built right on the bank, 100 meters above sea level. These are points of the Zemun loess plateau, an extension of the Syrmia loess plateau, which continues into the crescent-shaped Bezanijska Kosa loess hill on the south-east. The yellow loess is thick up to 40 meters and very fertile, with rich, grass-improved, humus chernozem. The uninhabited river islands of Great War Island and Little War Island on the Danube, also belong to the municipality Zemun, too.

In September 2018, Belgrade's mayor Zoran Radojicic announced that the construction of a dam on the Danube, in the Zemun-New Belgrade area, will start soon. The dam should protect the city during the high water levels. Such project was never mentioned before, nor it was clear how and where it will be constructed, or if it's feasible at all. Radojicic clarified after a while that he was referring to the temporary, mobile flood wall. The wall will be 50 cm (20 in) high and 5 km (3.1 mi) long, stretching from the Branko's Bridge across the Sava and the neighborhood of Ušce in New Belgrade, to the Radecki restaurant on the Danube's bank in the Zemun's Gardoš neighborhood. In case of emergency, the panels will be placed on the existing construction. The construction is scheduled to start in 2019 and to finish in 2020.