Irkutsk,  Russian: Иркутск, IPA:; Buryat and Mongolian: Эрхүү, Erhüü) 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.

Etymology

Irkutsk was named after the Irkut River. Its name was derived from the Buryat word for "spinning," and was used as an ethnonym among local tribes, who were known as Yrkhu, Irkit, Irgit, and Irgyt. The city was formerly known as Yandashsky after the local Tuvan chief Yandasha Gorogi.

The old spelling of the name of the city was «Иркуцкъ». Before the revolution, the city was called "East Paris", "Siberian Petersburg", "Siberian Athens". Locals like to think of their city as "middle of the earth".

In 1652, Ivan Pokhabov built a zimovye (winter quarters) near the site of Irkutsk for gold trading and for collecting fur taxes from the Buryats. In 1661, Yakov Pokhabov built an ostrog (a small fort) nearby. The ostrog gained official town rights from the government in 1686.

The first road connection between Moscow and Irkutsk, the Siberian Route, was built in 1760, and benefited the town economy. Many new products, often imported from China via Kyakhta, became widely available in Irkutsk for the first time, including gold, diamonds, fur, wood, silk, and tea. In 1821, as part of the Mikhail Speransky's reforms, Siberia was administratively divided at the Yenisei River. Irkutsk became the seat of the Governor-General of East Siberia.

In the early 19th century, many Russian artists, officers, and nobles were sent into exile in Siberia for their part in the Decembrist revolt against Tsar Nicholas I. Irkutsk became the major center of intellectual and social life for these exiles, and they developed much of the city's cultural heritage. They had wooden houses built that were adorned with ornate, hand-carved decorations. Many still survive today, in stark contrast with the standard Soviet apartment blocks that surround them.

By the end of the 19th century, the population consisted of one exiled man for every two locals. People of varying backgrounds, from members of the Decembrist uprising to Bolsheviks, had been in Irkutsk for many years and had greatly influenced the culture and development of the city. As a result, Irkutsk became a prosperous cultural and educational center in Eastern Siberia.

In 1879, on July 4 and 6, a fire burned out of control, destroying the palace of the Governor General, and the principal administrative and municipal offices. Many of the other public buildings, including the government archives, the library, and the museum of the Siberian section of the Russian Geographical Society, were completely ruined. Three-quarters of the city was destroyed, including approximately 4,000 houses. The city quickly rebounded, installing electricity in 1896. The first theater was built in 1897 and a major train station opened in 1898. The first train arrived in Irkutsk on August 16 of that year. By 1900, the city had earned the nickname of "The Paris of Siberia."

During the Russian Civil War, which broke out after the October Revolution, Irkutsk became the site of many furious, bloody clashes between the "White movement" and the "Bolsheviks", known as the "Reds". In 1920, Aleksandr Kolchak, the once-feared commander of the largest contingent of anti-Bolshevik forces, was executed in Irkutsk. This effectively destroyed the anti-Bolshevik resistance.

Irkutsk was the administrative center of the short-lived East Siberian Oblast, from 1936 to 1937. The city subsequently became the administrative center of Irkutsk Oblast, after East Siberian Oblast was divided into Chita Oblast and Irkutsk Oblast.

During the communist years, the industrialization of Irkutsk and Siberia in general was strongly encouraged. The large Irkutsk Reservoir was built on the Angara River between 1950 and 1959 in order to generate hydroelectric power and facilitate industrial development.

The Epiphany Cathedral, the governor's palace, a school of medicine, a museum, a military hospital and the crown factories are among the public institutions and buildings. The Aleksandr Kolchak monument, designed by Vyacheslav Klykov, was unveiled in 2004. On July 27, 2004, the Irkutsk Synagogue (1881) was gutted by a fire.

In December 2016, 74 people in Irkutsk died in a mass methanol poisoning, after drinking this toxic alcohol substitute.

In 2018, the BBC reported that men in Irkutsk had an average life span of only 63. The society had declined and their health had suffered markedly.

Irkutsk is twinned with:

•  Częstochowa, Poland
•  Eugene, United States
•  Gangneung, South Korea
•  Haute-Savoie, France
•  Kanazawa, Japan
•  Karlovy Vary Region, Czech Republic
•  Pforzheim, Germany
•  Pordenone Province, Italy
•  Prijedor, Bosnia and Herzegovina
•  Primorje-Gorski Kotar County, Croatia
•  Shenyang, China
•  Strömsund, Sweden
•  Ulaanbaatar, Mongolia
•  Vitebsk, Belarus