Petrozavodsk (Russian: Петрозаво́дск; Karelian/Vepsian/Finnish: Petroskoi) is the capital of the Republic of Karelia, Russia, with a population of 266,160 (2002 Census). It stretches along the western shore of the Lake Onega for some 27 kilometers. The city is served by Besovets Airport. Municipally, it is incorporated as Petrozavodsk Urban Okrug (Russian: Петрозаво́дский городско́й о́круг, Petrozavodsky gorodskoy okrug, Karelian: Petroskoin linnupiiri).

The city was founded on 11 September 1703 as Petrovskaya Sloboda by Prince Menshikov at the behest of Peter the Great who needed a new iron foundry for manufacturing cannons and anchors for the Baltic Fleet at the time of the Great Northern War. At first the foundry was named Shuysky zavod (literally, "factory at the Shuya River"), but a decade later its name was changed to Petrovsky zavod, after the reigning monarch. From this form the present name of the city derives.

By 1717, Petrovskaya Sloboda had grown into the largest settlement in Karelia, with about 3500 inhabitants, a timber fort, a covered market, and miniature palaces of the Tsar and Menshikov. The town's best known landmark was the wooden church of Sts. Peter and Paul, rebuilt in 1772 and renovated in 1789. The church retained its original iconostasis until this relic of Peter's reign was destroyed by fire on 30 October 1924.

After Peter's death, Petrovskaya Sloboda depopulated and the factory declined. It was closed down in 1734, although foreign industrialists maintained copper factories in the vicinity.

The industry was revived in 1773, when Catherine the Great established a new iron foundry upstream the Lososinka River. Designed to provide cannons for the ongoing Russo-Turkish Wars, the foundry was named Alexandrovsky, after Alexander Nevsky, who was considered a patron saint of the region. The factory was modernised and expanded under supervision of Charles Gascoigne in 1787-96. Local pundits claim that the first railway in the world (чугунный колесопровод) was inaugurated for industrial uses of the Alexandrovsky foundry in 1788.

During Catherine's municipal reform of 1777, Petrovskaya Sloboda was incorporated as a town, whereupon its name was changed to Petrozavodsk. A new Neoclassical city centre was then built, focused on the newly-planned Round Square. In 1784 Petrozavodsk was large enough to supplant Olonets as the administrative centre of the region. Although Emperor Paul abolished the Olonets Governorate, it was revived as a separate guberniya in 1801, with Petrozavodsk as its centre.

During the Finnish occupation of East Karelia in the Continuation War (1941–1944), the occupier chose to style the city Aanislinna (or Aaneslinna), rather than the traditional Petroskoi. The new name was a literal translation of Onegaborg, the name of a settlement marked on a 16th century map by Abraham Ortelius near the present-day city, Aaninen being the Finnish toponym for Lake Onega.

The city was occupied by Finnish troops for nearly three years before it was retaken by Soviet forces on June 28, 1944. Before leaving the town the Finnish troops provided the inhabitants with a week's ration of food; a unique deed in military history.