National Holiday in Thailand held annually on December 5.
If December 5 falls on a weekend, the holiday will be observed on the following Monday.
The day commemorates the birthday of the current King of Thailand, Bhumibol Adulyadej.
He is known as Rama IX, and has reigned Thailand since June 9 1946, making him the world's longest-serving current head of state and the longest-reigning monarch ever in Thailand's history.
Despite being a constitutional monarch, and not legally being allowed a role in politics, Bhumibol has made several decisive interventions in the Thai political sphere and has been credited with helping facilitate Thailand's transition to democracy in the 1990s.
The holiday itself is a colourful affair. Buildings across Thailand will display flags, bunting and portraits of the King, while around the Grand Palace area of Bangkok, the streets are decorated with thousands of marigolds.
In the evening, the streets around Ratchadamnoen and Sanam Luang are closed to traffic and many people come to watch celebratory fireworks displays.