Modern Sofia sits on continuous human habitation going back to at least 7000 BC. A Neolithic village in the Slatina district dates to the fifth or sixth millennium BC. Another Neolithic settlement near the modern National Art Gallery has been the traditional center of the city ever since. Thracian tribes, the Tilataei, were the earliest known inhabitants. They were absorbed into the Odrysian kingdom in the 500s BC. Philip II of Macedon, the father of Alexander the Great, destroyed the town in 339 BC. Then came the Celtic Serdi, who gave the city the name it would keep for the next two millennia: Serdica, the city of the Serdi. The Roman general Crassus subdued them in 29 BC and the city entered the empire. It thrived. Two Roman emperors, Aurelian and Galerius, were born here. Galerius issued the Edict of Toleration here in 311, the first edict that legally permitted Christianity in the Roman Empire, two years before the more famous Edict of Milan.

The Huns destroyed the city in 447 and it lay in ruins for a century before Justinian rebuilt it. In 809 the Bulgarian khan Krum incorporated Sredets, as the Slavs were now calling it, into the First Bulgarian Empire. The Byzantines took it back in 1018 and held it until 1194. Throughout these centuries the city kept its old Slavic name, the word for middle, until something curious happened in the 14th century. People started referring to the city by the name of its great church, the Hagia Sophia. The Greek word sophia means wisdom. By 1359 the new name appears in a dialogue between two merchants from Dubrovnik. The 14th-century Vitosha Charter of Tsar Ivan Shishman uses it. Ragusan merchant notes from 1376 use it. The Ottomans, when they captured the city in 1382 or 1385, came to favor the form Sofya. Even after liberation in 1878, when there was a brief debate about restoring the Slavic name Sredets, a compromise emerged: Sofia for state institutions, Sredets for administration and the Church, until eventually only Sofia remained.

Lala Sahin Pasha besieged Sredets for three months before it fell to him in the 1380s. The commander left a description of the garrison that has the ring of grudging respect: heavily built, mustached, war-hardened soldiers who liked their wine and rakia. From 1530 the city served as capital of the beylerbeyate of Rumelia, the Ottoman province that administered all the empire's European lands, the Balkans entire. Sofia was the largest export base in modern Bulgaria for the Ragusan caravan trade. Sixteenth-century sources describe a city of eight Friday mosques, three public libraries, twelve churches, three synagogues, and the largest bedesten market in the Balkans. The population was extraordinarily mixed: Muslims, Bulgarian and Greek Orthodox Christians, Armenians, Georgians, Catholic Ragusans, Romaniote and Ashkenazi and Sephardi Jews, Romani people. Then a slow decline set in during the 17th century, accelerated by the chaos of the late 18th and early 19th centuries when local Ottoman warlords ravaged the countryside, until the seat of provincial government moved to Bitola in 1826.

When Russian forces under General Iosif Gurko approached Sofia during the Russo-Turkish War of 1877-78, the Ottoman commander Suleiman Pasha threatened to burn the city in defense. Four foreign residents refused to leave. The French diplomat Leandre Legay, the Italian Vito Positano, the chief rabbi Gabriel Almosnino, and the Austrian consular agent Josef Valdhart stayed in place when most foreigners would have fled. Their presence saved Sofia from being torched. Most of the mosques were destroyed in the war regardless, including seven of them in a single night in December 1878 when a thunderstorm masked the noise of explosions arranged by Russian military engineers. Following the war, the great majority of the Muslim population departed. The Russians liberated Sofia on 4 January 1878. Marin Drinov proposed it as the capital of the new Bulgarian state on 3 April 1879. At the time of liberation the population was 11,649, down from a height of 70,000 in the late 18th century.

Sofia is now the 14th-largest city in the European Union, with around 1.28 million residents in the city proper and 1.6 million in the metropolitan region. It is one of the highest European capitals at 550 meters elevation, surrounded on every side by mountains: Vitosha to the south, Lyulin to the west, the Balkan range to the north. There are 49 mineral and thermal springs in and around the city, fed by the volcanic geology beneath the valley. The city has been called a triangle of religious tolerance because the Sveta Nedelya Church, the Banya Bashi Mosque, and the Sofia Synagogue stand within walking distance of each other. The triangle was recently upgraded to a square with the inclusion of the Catholic Cathedral of St Joseph. The Boyana Church, with its 13th-century frescoes that anticipate the Italian Renaissance, has been a UNESCO World Heritage Site since 1979. The Rotunda of St George, a 4th-century Roman building, is the oldest standing structure in Sofia, still hosting Eastern Orthodox services.

Vitosha Boulevard, the pedestrian shopping street locals call Vitoshka, runs from the city center toward the mountain that gives the boulevard its name. Cafes and restaurants spill onto the sidewalk in summer, and on clear winter days the snow line on Vitosha is visible at the boulevard's southern end. The mountain itself, twenty minutes from downtown by car, has skiing on its upper slopes and hiking trails year-round, though the resort infrastructure has decayed in recent decades due to disputes between the private operator and the municipality. The city center contains continuously visible remnants of ancient Serdica beneath plate-glass floors and in dedicated archaeological complexes near the Sheraton Hotel and the Presidency. The Forbes magazine listed Sofia among the top 10 cities globally to launch a startup, citing low corporate tax, fast internet, and the presence of investment funds. Air pollution remains a serious problem in winter, when temperature inversions trap particulate matter from solid fuel heating in the valley.