The Kings birthday is a National Holiday in Thailand held annually on 5 December unless this is a weekend when the holiday will be observed on the following Monday. If you are visiting Thailand at this time, it is worth noting that all Government offices and banks (except those in shopping malls) will be closed.

The day commemorates the birthday of the late King of Thailand, Bhumibol Adulyadej (known as Rama IX) who reigned Thailand since 9 June 1946, making him the world's longest-serving head of state and the longest-reigning monarch in Thailand's history.

Despite being a constitutional monarch (much like the Queen of England) and not legally being allowed a role in politics, Bhumibol made several decisive interventions in the Thai political sphere and has been credited with helping facilitate Thailand's transition to a democracy in the 1990s.

The holiday itself is a colourful affair with buildings across Thailand display flags, bunting and portraits of the King, and in the Grand Palace area of Bangkok, the streets are decorated with thousands of marigolds, chosen for their colour – yellow. In Thai culture each day has a colour association and yellow is the colour for Monday, the day on which the King was born.

In the evening, the streets around Ratchadamnoen and Sanam Luang are closed to traffic and many people come out to celebrate and to watch the fireworks displays.