Buddhist Lent begins on Asarnha Bucha Day. The following day is Khao Pansaa (meaning "entering the Rainy Season"). It begins a period of what Christians might call "retreats" by Buddhist monks. This period is known in English as Buddhist Lent as it is a period of renewal, meditation and learning, as well as when Buddhists make moral resolution such as to refrain from smoking, drinking alcohol and the like or to observe more rigorously the five major precepts of Buddhism. This three month period begins on the first full moon of the Buddhist Lunar calendar during the eighth month of every year. The Lenten period ends in Mid October with Ouk Pansaa, meaning "leaving the Rainy Season".

On Khao Pansaa Day monks are presented with candles and robes. The gift of candles is a tradition which arose when candles were essential for both ceremonies and studying scriptures. Schools and universities together with public and private organisations will arrange colourful candle lit processions leading to a temple where the offering of the candles will be made. Khao Pansaa marks the religious beginning of the Rainy Season. During this period the monks usually return to the temple where they were ordained, staying for approximately three months. The monks are not permitted to leave the temples to stay overnight at any other location during these months.

Traditionally this observance began as monks travelling during the rainy season felt it inappropriate to walk at this time as many small living creatures were about and the newly sown rice crops were in the ground and they wished to harm neither by stepping on them. It was also, of course, a time of inclement weather. Therefore, it was established that monks would remain in temples for three months discussing and studying Buddhist scriptures, following Buddhist disciplines, meditating and performing ritual ceremonies.

The custom of Khao Pansaa has continued with three classes of ceremonies, a Royal ceremony conducted by the King of Thailand, ritual ceremonies for devout followers of Buddhism throughout the Kingdom and ceremonies performed by monks in the localo temples.

Followers of Buddhism all over Thailand will attend temples in the morning bringing food, items like cleaning products, money, the traditional candles, garments and ceremonial items for the monks.

It is also a day on which many new monks are ordained with great ceremony. These novices take the vows for periods of up to the three months with some staying even longer. Senior monks at each monastery perform other ceremonies leading followers in worship and prayer.

Unlike in Western cultures, to enter the monkhoods in Thailand is not a life-long commitment, rather, for most, it is a period of spiritual training, to gain merit for themselves and their parents, and to conform to the belief that a man who has not been a monk cannot be considered a mature adult.

A Buddhist ordination ceremony is a mixture of religious solemnity, merit-making and boisterous celebration as Thais believe that the three most important events of a man's life are his birth, his ordination and his marriage. Socially, the ordination is something in which the entire community participates. Villagers gain merit by accompanying the tonsured, white-robed candidate for monkhood in a colourful procession to the monastery. The procession is often marked by joyous dancing and the beat of long drums. It is not a quiet event.

Candle festivals are held annually on this day. Sculpted beeswax candles, generally depicting mythological creatures, are carried in a ceremonial parade in each province before being presented to local temples. The most famous of these is in Ubon Ratchathani Province.

Khao Pansaa, is recognized as a government holiday with many others taking time from the work place. Everyone is invited to participate in the temple ceremonies and to refrain from offensive behaviour for the day and thereafter.

While government offices, banks and major businesses will be closed major shopping centres will be open. Money Exchange booths of banks will also be open. Places of entertainment will either be closed or only offering non-alcoholic refreshment.