Knjaževac (Serbian Cyrillic: Књажевац, pronounced [kɲǎːʒɛʋats]) is a town and municipality situated in eastern Serbia, in the Timočka Krajina region bordering Bulgaria. The town is situated between three mountains. The municipality has a population of 30,902 inhabitants.

In the Roman period, Timacum Maius existed within the present municipality. In 1833, the town, formerly known as Gurgusovac, was liberated from the Ottoman Empire and was administrated into the Krajina nahija of the Principality of Serbia in 1834. In 1859 the official name was changed to Knjaževac. In 1944, a train tunnel was built in the town, which is depicted in the town's coat of arms.

The municipality extends over an area of 1202 km² and is the fourth largest in the Republic of Serbia. Its countryside is mostly hilly and mountainous.

The highest point in the territory of the municipality is Midžor on Stara Planina (2169 m), which is also the second highest peak in the Republic of Serbia. The lowest point is 176 metres high and is situated in the Knjaževac valley. There are 86 inhabited places in the municipality of which 85 are villages. The town itself is situated at the confluence of the Trgoviški Timok and the Svrljiški Timok which become the Beli Timok. It flows on towards Zaječar, merges with the Crni Timok and becomes simply, Timok. It is this river that gives name to the Timočka Krajina region.