Mixed reactions to Putin's speech in Crimea and Ukraine
18 March 2014 Last updated at 20:05 GMT
Russian President Vladimir Putin and the leaders of Crimea signed a bill to absorb the peninsula into Russia.
Mr Putin told Russia's parliament that Crimea had "always been part of Russia" and in signing the treaty he was righting an "historical injustice".
The BBC's Mark Lowen reports from Lenin Square in the Crimean city of Simferopol where there have been celebrations.
Meanwhile in Independence Square, Kiev, Ukraine, Chris Morris says that "people won't be in a mood to take a history lesson here".