Turku ( TOOR-koo; Finnish: [ˈturku] (listen); Swedish: Åbo, Finland Swedish: [ˈoːbu] (listen)) is a city and former capital on the southwest coast of Finland at the mouth of the Aura River, in the region of Finland Proper (Varsinais-Suomi) and the former Turku and Pori Province (Turun ja Porin lääni; 1634–1997). The region was originally called Suomi (Finland), which later became the name for the whole country. As of 31 March 2021, the population of Turku was 194,244 making it the sixth largest city in Finland after Helsinki, Espoo, Tampere, Vantaa and Oulu. There were 281,108 inhabitants living in the Turku Central Locality, ranking it as the third largest urban area in Finland after the Capital Region area and Tampere Central Locality. The city is officially bilingual as 5.2 percent of its population identify Swedish as a mother-tongue.

It is unknown when Turku gained city rights. The Pope Gregory IX first mentioned the town Aboa in his Bulla in 1229 and the year is now used as the foundation year of Turku. Turku is the oldest city in Finland, and served as the most important city of the eastern part of the Kingdom of Sweden (modern-day Finland). After the Finnish war, Finland became an autonomous grand duchy of the Russian Empire in 1809, and Turku was made the capital of the grand duchy. However, Turku lost its status as capital only after three years in 1812, when Tsar Alexander I of Russia decided to move the capital to Helsinki. It was only after the last great fire in 1827 that most governmental institutions were moved to Helsinki along with the Royal Academy of Turku (Turun Akatemia) founded in 1640, which then became the University of Helsinki, thus consolidating Helsinki's position as the new capital. Turku continued to be the most populous city in Finland until the end of the 1840s, and it remains the regional capital and an important business and cultural center and port.

Because of its long history, it has been the site of many important events, and has extensively influenced Finnish history as the former capital city. Along with Tallinn, the capital city of Estonia, Turku was designated the European Capital of Culture for 2011. In 1996, it was declared the "Christmas City" of Finland. Also, Turku has been officially declared the Food Capital of Finland, because it holds a number of Finland's oldest, highest quality restaurants alongside a historically famous fish market, held twice a year. Turku's canteen and café culture has often been compared to French food culture, which is why Turku has also been perceived as "Paris of Finland"; this is also the reason for the Swedish saying: "Varför Paris, vi har ju Åbo!" ("Why Paris, we have Turku!")

Due to its location, Turku is a notable commercial and passenger seaport with over three million passengers traveling through the Port of Turku each year to Stockholm and Mariehamn.