Known in Estonia as Suveräänsuse deklareerimise päev, this annual independence celebration commemorates the Declaration on the Sovereignty of the Estonian SSR (Deklaratsioon Eesti NSV suveräänsusest) issued on November 16, 1988, during the "Singing Revolution." The declaration asserted Estonia's sovereignty and laws over the authority of the Soviet Union. Estonia subsequently joined the European Union and became a member of NATO in 2004.