The resulting stand-off between Russia and the West has brought relations between the two sides to their lowest since the Cold War.
Washington accuses Moscow of coordinating the unrest in eastern Ukraine, though Russia denies this. Moscow made similar denials over Crimea until Russian President Vladimir Putin acknowledged his troops had acted alongside local militia.
* Nov 21: Kiev suddenly announces suspension of trade and association talks with the EU and opts to revive economic ties with Moscow, triggering months of mass rallies in Kiev.
* Nov 30: Riot police try to break up the Kiev demonstration by force. Protest turns against Yanukovich and his government.
Protests continue with crowds of up to 800,000. Some clashes with police. Opposition forms bloc called Maidan.
Yanukovich and Putin meet, Putin agrees to buy $15 billion of Ukrainian debt and to slash by a third the price of Russian gas supplies to Ukraine.
* Jan 22: Three people die in protests in Kiev. EU threatens action over crisis. Talks between opposition, Yanukovich fail.
* Jan 23: Washington threatens sanctions over violence.
* Jan 26: Unrest spreads to pro-Yanukovich east.
Anti-government protests turn increasingly violent. At least 77 people killed in clashes between demonstrators and police.
* Feb 21: Opposition leaders sign EU-mediated peace pact with Yanukovich.
* Feb 22: Ukraine's parliament votes to remove Yanukovich, who flees. Arch-rival Yulia Tymoshenko released from jail.
* Feb 26: Ukraine appoints new government. Angry Russia puts 150,000 troops on high alert.
* Feb 27-28: Armed men seize Crimea parliament, raise Russian flag. Militia take control of two airports in Crimea.
* March 1: Putin wins parliamentary approval to invade Ukraine, angering the White House. Russian forces fan out in Crimea.
* March 6: Crimea's leadership votes to join Russia. U.S. President Barack Obama orders sanctions on those responsible for Moscow's actions in Ukraine.
EU leaders hold emergency summit to find ways to pressure Russia to back down and accept mediation.
* March 15: Two killed in clashes between pro-Russian demonstrators and Ukrainian nationalists.
* March 16: Referendum held in Crimea, shows overwhelming support for joining the Russian Federation.
* March 21: Putin signs laws completing annexation of Crimea. The U.S. imposes sanctions on Putin's close allies, EU follows with similar measures.
* March 23: NATO says Russia has amassed a large force at Ukraine's border.
* March 24: Ukraine pulls troops from Crimea.
* April 2: NATO suspends cooperation with Russia.
* April 7: Pro-Russia activists in eastern Ukraine proclaim the creation of the "Donetsk People's Republic".
* April 12: Separatists take control of city of Slaviansk in eastern Ukraine. Kiev prepares troops.
* April 13: One Ukrainian state security officer killed and five wounded in operation against separatists.
* April 14: Obama warns Putin in phone call that Moscow would face further costs for its actions in Ukraine.
* April 17: Pro-Russian separatists seize armoured vehicles of Ukraine forces trying to recapture rebel-controlled town.
* April 18: The United States, Russia, Ukraine and the EU reach deal for illegal armed groups to disarm and end occupations of public buildings and spaces.
* April 19: Separatists say they will not sign deal until the Kiev government steps down.
* April 24: Ukraine sends in troops again to try to expel the separatists in Slaviansk, kill five rebels.
* April 25: Ukrainian forces mount full blockade of Slaviansk. Separatists detain group of international observers, say a Kiev "spy" among them.
* April 26: G7 leaders agree to impose extra sanctions on Russia over Ukraine.