Today is Poland's national holiday, to commemorate The Constitution of May 3, 1791.
It was first declared a holiday (May-3rd-Constitution Day - Swieto Konstytucji 3 Maja) on May 5, 1791.
Banned during the Partitions of Poland, it again became a holiday in April 1919 under the Second Polish Republic.
The May 3rd holiday was banned once more during World War II by the Nazi and Soviet occupiers.

After the 1946 anti-communist student demonstrations, it lost support with the authorities of the Polish People's Republic, who replaced it with May 1 Labor Day celebrations.
May 3rd lost its legal standing as a holiday in January 1951. Until 1989, May 3rd was a common day for anti-government and anti-communist protests.

It was restored as an official Polish holiday in April 1990, after the fall of communism.

The May 3rd, 1791 Constitution was the first liberal constitution in Europe and the second in the world, after the Constitution of the United States.