Tens of thousands of people have died since Putin sent in the troops in 2022.
Ukraine’s president has spoken of 46,000 Ukrainian military deaths, but open source site ualosses.org suggests the number is close to 74,000.
More than 12,900 civilians have lost their lives in Ukraine, according to the UN, which says the true toll is likely far higher.
Russia rarely admits to military losses, but BBC analysis estimates that Russian deaths could range from 164,223 to 237,211.
The war has forced 6.9 million Ukrainians to seek refuge abroad, and a further 3.8 million to flee their homes inside Ukraine.
At the start, Putin did not even call it war but a “special military operation”. Eventually in 2024 he accepted it was a war, but claimed it had been instigated by Kyiv or its “Western handlers”.
What are the historical ties between Ukraine and Russia?
Putin appears to believe that Ukraine should remain in Russia’s sphere of influence because of the historical links between the two countries.
From 1922 to 1991 Ukraine was part of the Soviet Union and many Ukrainians speak Russian, especially in the east, and including Volodymyr Zelensky who is a native speaker.
Many Russians view Crimea as their own. It was annexed by Catherine the Great in 1783 and handed to Ukraine by Soviet leader Khrushchev in 1954. Ten years earlier, his predecessor Stalin had deported Crimea’s Tatar population, so the majority population was ethnic Russian.
Since 1991 Ukraine has been an independent state. It abandoned its nuclear weapons in 1994 in return for guaranteed security from Russia, the UK and US which Moscow failed to respect.
Since the war, many Ukrainians have turned their back on Russian, and Zelensky himself avoids using the language in public.