Held in the middle of May every year, the festival takes place on different days throughout the month in all parts of Laos.

Bun Bang Fai originates from ancient times when ethnic Lao people believed in many gods and is mentioned in tales, such as ‘The Tale of Pha Daeng–Nang Ai’ and ‘The Tale of Phaya Khankhak’. These stories refer to the firing of rockets to the heavens to communicate with the God of Rain and persuade him to send the rains in the earth in a timely fashion for cultivation. 

Today in Laos, Bun Bang Fai is held over the sixth Lunar month, usually around May and June, coinciding with the plantation and the beginning of the rainy seasons. Several months before the festival, an organizing committee is formed in each future host village to discuss all aspects of the festival, including inviting other villages, establishing rules and safety measures and setting criteria and prizes for the best rockets. 

The festival usually lasts two days and begins early in the morning with the associated religious ritual by the monks in the temple. Early in the afternoon, a Buddhist procession kicks off in which villagers carrying money trees circle three times the central ordination hall where sits a buddha statue in a clockwise rotation to the sound of traditional music. The money trees are then offered to the monks in a Buddhist ritual believed to garner religious merit. Afterward, rockets from all involved villages are displayed in the court of the temple followed by a celebration with traditional music and dance that can last up to the early morning of the next day.

The second day begins with a morning ceremony of food offering from faithful villagers to the monks in the assembly hall of the temple. he food usually includes sticky rice, cakes, and other sweets that the faithful line up to place in the monks’ alms-bowls during the sermon. In addition, other food dishes are portioned out in small bowls and are offered to the monks on rattan trays. After the ceremony a meal is shared by all participants. The faithful believe these offerings grant long life to anyone who gives with a serene heart.

The religious ceremony is followed by a boisterous street parade through the village with floats and pickup trucks displaying the rockets on the sound of the Khene, long drums and cymbals. Teams of contestants dance and chant traditional folksongs, with the team’s leader chanting first and then the others repeating. Rockets firing contest is the highlight of the festival. The higher and farther the rocket shot, the higher the score and the more compliments received. These rockets are mainly contributed by villages or by individuals and businesses to pray for luck in the next year.

In most of Laos, the festival remains largely a community affair that brings people from different villages. It promotes unity and friendship within and among village communities and helps maintain their close relationships.

According to Wikipedia.