Irkutsk is the largest city and administrative center of Irkutsk Oblast, Russia. With a population of 617,473 as of the 2010 Census, Irkutsk is the 25th largest city in Russia by population, the 5th largest in the Siberian Federal District, and one of the largest cities in Siberia.

Located in the south of the eponymous oblast, the city proper lies on the Angara River, a tributary of the Yenisei, about 850 kilometres (530 mi) to the south-east of Krasnoyarsk and about 520 kilometres (320 mi) north of Ulaanbaatar. The Trans-Siberian Highway (Federal M53 and M55 Highways) and Trans-Siberian Railway connect Irkutsk to other regions in Russia and Mongolia.

Many distinguished Russians were sent into exile in Irkutsk for their part in the Decembrist revolt of 1825, and the city became an exile-post for the rest of the century. Some historic wooden houses still survive. When the railway reached Irkutsk, it had earned the nickname of "The Paris of Siberia." The city was the center of bitter fighting in the Russian Civil War of 1918-20. Afterward, in the Soviet period, its architecture was dominated by the mandatory squared-up style. The city became a major centre of aircraft manufacture. The historic centre of Irkutsk is located on UNESCO's tentative list of World Heritage Sites.