Irkutsk is a city in Russia, the administrative center of Irkutsk Oblast, and forms the Irkutsk Urban Okrug.

 The city has a population of 605,708 (2025), making it the sixth most populous city in Siberia and the twenty-fifth most populous city in Russia.

 It is located in Eastern Siberia, on the banks of the Angara River, at the confluence of the Irkut River, and is 66 kilometers away from Lake Baikal. The climate is sharply continental, with significant temperature fluctuations. Due to its proximity to the seismically active Baikal Rift, there are regular minor earthquakes.

 It is a major scientific and educational center. The main industries include aircraft manufacturing, hydropower, and food production. It is a transportation hub on the Trans-Siberian Railway and the Baikal and Siberia federal highways.

 It was founded as a fortress in 1661. It was severely damaged by a fire in 1716. The next major fire in 1879 caused such severe destruction that it took more than 10 years to fully rebuild the city.