Beyoğlu (Turkish: [ˈbejoːɫu]) is a municipality and district of Istanbul Province, Turkey. Its area is 9 km², and its population is 225,920 (2022). It is on the European side of Istanbul, Turkey, separated from the old city (historic peninsula of Constantinople now known as Fatih) by the Golden Horn.

Genoese traders founded Beyoğlu. Beyoğlu's population was mostly foreign and of European background in the 19th century. Events such as 1950s Istanbul pogrom and suburbanization led to high income Muslims, Armenians, Greeks, and Jews leaving for the suburbs, which resulted in decaying housing. Urban renewal projects and gentrification started in 1980s and 1990s. Cultural events such as Istanbul Film Festival, restaurants, and coffee shops were established, while middle-income and upper-income residents returned to the area. Present-day Beyoğlu is one of the main night-life areas in Istanbul.

The district encompasses other neighborhoods located north of the Golden Horn, including Galata (modern-day Karaköy), Tophane, Cihangir, Şişhane, Tepebaşı, Tarlabaşı, Dolapdere and Kasımpaşa, and is connected to the old city center across the Golden Horn through the Galata Bridge, Atatürk Bridge and Golden Horn Metro Bridge. Beyoğlu is also home to İstiklal Avenue and Taksim Square.

Beyoğlu continued to be named Pera during the Middle Ages and, in western languages, into the early 20th century.^{[citation needed]} Pera (Greek: Πέρα) means "beyond" in Greek.^{[citation needed]}

According to the prevailing theory, the Turkish name of Pera, Beyoğlu, meaning "Bey's Son" in Turkish, is a modification by folk etymology of the Venetian title of Bailo. The 15th century ambassador of Venice in Istanbul, Andrea Gritti (who later became the Doge of Venice in 1523) had a mansion in this area. His son Alvise Gritti, who had close relations with the Sublime Porte, also stayed there and was probably the person who was specifically referred to as Bey Oğlu after his father became the Doge of Venice. Located further south in Beyoğlu and originally built in the early 16th century, the "Venetian Palace" was the seat of the Bailo. The original palace building was replaced by the existing one in 1781, which later became the Italian Embassy following Italian unification in 1861, and the Italian Consulate in 1923, when Ankara became the capital of the Republic of Turkey.

The area now known as Beyoğlu has been inhabited since Byzas founded the City of Byzantium in the 7th century BC, and predates the founding of Constantinople. During the Byzantine era, Greek speaking inhabitants named the hillside covered with orchards Sykai (The Fig Orchard), or Peran en Sykais (The Fig Field on the Other Side), referring to the "other side" of the Golden Horn. As the Byzantine Empire grew, so did Constantinople and its environs. The northern side of the Golden Horn became built up as a suburb of Byzantium as early as the 5th century. In this period the area began to be called Galata, and Emperor Theodosius II (reigned 402–450) built a fortress. The Greeks believe that the name comes either from galatas (meaning "milkman"), as the area was used by shepherds in the early medieval period, or from the word Galatai (meaning "Gauls"), as the Celtic tribe of Gauls were thought to have camped here during the Hellenistic period before settling into Galatia in central Anatolia, becoming known as the Galatians. The inhabitants of Galatia are famous for the Epistle to the Galatians and the Dying Galatian statue. The name may have also derived from the Italian word Calata, meaning "downward slope", as Galata, formerly a colony of the Republic of Genoa between 1273 and 1453, stands on a hilltop that goes downwards to the sea.

The area came to be the base of European merchants, particularly from Genoa and Venice, in what was then known as Pera. Following the Fourth Crusade in 1204, and during the Latin Empire of Constantinople (1204–1261), the Venetians became more prominent in Pera. The Dominican Church of St. Paul (1233), today known as the Arap Camii, is from this period.

In 1273 the Byzantine Emperor Michael VIII Palaiologos granted Pera to the Republic of Genoa in recognition of Genoa's support of the Empire after the Fourth Crusade and the sacking of Constantinople in 1204. Pera became a flourishing trade colony, ruled by a podestà.