Valjevo (Serbian Cyrillic: Ваљево, pronounced [ʋâːʎeʋo]) is a city and the administrative center of the Kolubara District in western Serbia. According to the 2022 census, the city itself has a population of 56,145 while the city administrative area has 82,169 inhabitants. The city is situated along the river Kolubara.

In the nearby village of Petnica, scientists found the first complete neolithic habitat in Serbia and dated it at 6,000 years old. In Roman times this area was part of the province of Moesia. Valjevo was mentioned for the first time in 1393. It was an important staging post on the trade route that connected Bosnia to Belgrade.

During Ottoman rule, according to Matija Nenadović, there were 24 mosques in Valjevo in the late 18th century.

At the beginning of the 19th century most of the territory of Serbia rapidly transformed. The Serbian revolution began with armed rebellion. In 1804, the local Serb population had rebelled against the Turkish lords and liberated a large part of Serbia. One cause for the revolution was the killing of two prominent Serbian commanders by the Ottoman Turks. The two well-known knights, Ilija Birčanin and Aleksa Nenadović, were beheaded in Valjevo on the bridge over the Kolubara.

The settlement's development accelerated further in the 20th century, when Valjevo became an important industrial and cultural center. During the First World War the battle of Kolubara was fought in the immediate vicinity. A large hospital for the wounded was in the town. One of the captured partisan leaders Stjepan Filipović was executed by the Nazis in Valjevo in 1942.

In 1999, Valjevo was repeatedly bombed during the NATO intervention in Yugoslavia.

Apart from the city, Valjevo covers the administrative area which includes the following settlements:

According to the 2022 census, the city proper has a population of 56,059, while the administrative area has a population of 82,169.