Koninginnedag ( pronunciation (help·info)) or Queen's Day is a national holiday in the Kingdom of the Netherlands. Celebrated on 30 April (the 29th if the 30th falls on a Sunday), Koninginnedag is Queen Beatrix's official celebration day. Though Queen Beatrix was born on 31 January, the holiday is observed on 30 April as it was the birthday of her mother and predecessor, Juliana. Many of the traditional activities are held outside, and observing the holiday in April makes suitable weather more likely.

From 1 May 2017 onwards, Saba and Sint Eustatius will be celebrating their own Koninginnedag on 30 April (29 April if 30th is a Sunday and 1 May if 30th is a Friday).

The holiday was first observed on 31 August 1885 as Prinsessedag or Princess's Day, the fifth birthday of Princess Wilhelmina, heiress to the Dutch throne. On her accession, the holiday acquired its present name, Koninginnedag. When held on 31 August the holiday was the final day of school summer vacation, leading to its popularity among children. Following the accession of Wilhelmina's daughter Queen Juliana in 1948, the holiday was moved to her birthday. Her daughter, Beatrix retained the celebration on 30 April after she took the throne in 1980. Beatrix altered her mother's custom of receiving a floral parade near a royal palace, instead choosing to visit different Dutch towns each year and join in the festivities. In 2009, the Queen was carrying out this custom in the town of Apeldoorn when a car was driven into a crowd surrounding the royal family's vehicle; seven people in the crowd were killed, and the car's driver also died soon afterwards.