Knjaževac (Књажевац) is a town and municipality situated in the eastern part of Serbia bordering the Republic of Bulgaria and is part of Timočka Krajina region. It is found between the latitudes of 43°20' and 43°45' north and between the longitudes 22°11' and 22°41' east. The town is situated between three mountains.

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 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.

Knjaževac is connected with other towns by road and railroad traffic.

The population of the municipality of Knjaževac is 37,172, while the population of the town is 19,351 (2002 census). According to the previous census from 1991, the population of the municipality was 44,036, and the population of the town was 19,705. The average population density is 36 inhabitants per square kilometer making it a sparsely populated municipality.

Knjaževac and its surroundings have a temperate and continental climate. The warmest month is July with an average temperature of 21.3°C, whereas the coldest month is January with average temperature of –0.8°C. Average annual rainfall is 590.8 mm/m2. There are 306 sunny days and 30 days of snow in a year.