Since 2004, August 23 is celebrated as the Day of the National Flag in Ukraine. The first ceremonial raising of the yellow-and-blue Ukrainian flag in modern times took place on 24 July 1990 at the flagstaff of the Kiev City Council, two years before the flag was officially adopted as the National flag of the Ukrainian state (1992).
Combination of blue and yellow as a symbol of Ukrainian lands comes from the flag of the Kingdom of Galicia–Volhynia used in 12th century. As a national flag, the blue and yellow bicolor has been officially used since the 1848 Spring of Nations when it was hoisted over the Lviv Rathaus. It was officially adopted as a state flag for the first time in 1918 by the short-lived West Ukrainian People's Republic, and subsequently used by the Ukrainian People's Republic. When Ukraine was part of the Soviet Union, the flag was outlawed and before 1949 there was no official state flag until adoption of the red-blue flag of the Ukrainian SSR. The blue and yellow flag was provisionally adopted for the official ceremonies in September 1991 following Ukrainian independence, before finally officially being restored on 28 January 1992 by the parliament of Ukraine. The common explanation of the colors of the flag is "blue sky above yellow field of wheat".