June 21: June Solstice (17:16 UTC, 2011); International Surfing Day; National Aboriginal Day in Canada
- 217 BC – Second Punic War: The Carthaginians under Hannibal executed one of the largest military ambushes in history when they overwhelmingly defeated the Romans.
- 1826 – Greek War of Independence: A combined Egyptian and Ottoman army began their invasion of the Mani Peninsula, but they were initially held off by the Maniots at the fortifications of Vergas.
- 1919 – Admiral Ludwig von Reuter scuttled the German High Seas Fleet in Scapa Flow to prevent the ships from being seized and divided amongst the Allied Powers.
- 1948 – The Manchester Small-Scale Experimental Machine, the world’s first stored-program computer, ran its first computer program.
- 2004 – SpaceShipOne (pictured) completed the first privately funded human spaceflight.