Niš is the third largest city in Serbia and the administrative center of the Nišava District. According to the 2011 census, the city proper has a population of 183,164, while its administrative area has a population of 260,237 inhabitants.

Several Roman emperors were born in Niš or used it as a residence: Constantine the Great, the first Christian emperor and the founder of Constantinople, Constantius III, Constans, Vetranio, Julian, Valentinian I, Valens; and Justin I. Emperor Claudius Gothicus decisively defeated the Goths at the Battle of Naissus (present-day Niš). Later playing a prominent role in the history of the Byzantine Empire, the city's past would earn it the nickname The Emperor's City.

After about 400 years of Ottoman rule, the city was liberated in 1878 and became part of the Principality of Serbia, though not without great bloodshed—remnants of which can be found throughout the city. Today, Niš is one of the most important economic centers in Serbia, especially in the electronics, mechanical engineering, textile, and tobacco industries. Constantine the Great Airport is Niš's international airport. The city is also the seat of the University of Niš, the Eparchy of Niš and the Command of Serbian Army.

In 2013, the city was host to the celebration of 1700 years of Constantine's Edict of Milan.

Tourist sites include:

• Cegar - The place where Battle on Cegar Hill took place on 19 May 1809.
• Crveni Krst concentration camp - One of the few preserved Nazi concentration camps in Europe. It is on 12 February Boulevard.
• Memorial to Constantine the Great - built in the city centre in 2013, in commemoration to Constantine the Great who was born in the city, on the anniversary of the Edict of Milan.
• Bubanj - Monument to fallen Yugoslav World War II fighters, forming the shape of three clenched fists. The place where 10,000 civilian hostages from Niš and south Serbia were brutally murdered by German Nazis.
• Kalca, City passage and Gorca - Trade centers situated in Milana Obrenovica Street.
• Memorial Chapel in the memory of NATO bombing victims - The chapel was built by local authorities while the monument was built by the State government in 1999. They are situated in Sumatovacka street near Niš Fortress.
• Niš Fortress - The remaining fortification was built by the Turks, and dates from the first decades of the 18th century (1719-23). It is situated in the city center.
• The fortress-cafes - They are situated near Stambol gate (the main gate of the fortress).
• Mediana - Archeological site, an Imperial villa, from the late Roman period on the road leading to Sofia, Bulgaria, near EI Nis.
• Niška Banja (Niš spa) - A very popular spa during the summer season. It is 10 km (6 mi) from city center on the road leading to Sofia, in the bottom of Suva Planina Mountain.
• Tinkers Alley - An old urban downtown zone in today's Kopitareva Street, built in the first half of the 18th century. It was a street full of tinkers and other craftsmen, but today it is packed with cafes and restaurants.
• Skull Tower (Cele Kula) - A monument to the Serbian revolutionaries (1804-13); a tower made out of skulls of Serbian uprisers, killed and decapitated by the Ottomans. It is situated on Zoran Ðindic Boulevard, on the old Constantinople road leading to Sofia.
• Sultans Trail Long distance hiking and biking route from Vienna to Istanbul runs through Niš.