Vesak is an annual holiday observed by practicing Buddhists in many Asian countries like Thailand, Cambodia, Sri Lanka, Malaysia, Myanmar, Singapore, Vietnam, and also Indonesia, Hong Kong, and Taiwan.
In Mahayana Buddhist traditions, the holiday is known by its Sanskrit equivalent, Vaiśākha. The word Vesak itself is the Sinhalese language word (වෙසක්) for the Pali variation, "Vesākha". Vesak is also known as Visaka Bochea in Cambodia, Visakah Puja, Buddha Purnima or Buddha Jayanti in India, Bangladesh and Nepal, Visakha Bucha in Thailand, Phật Đản in Vietnam, Waisak in Indonesia, Vesak (Wesak) in Sri Lanka and Malaysia, 佛誕 (fó dàn) in Chinese-speaking countries, and Saga Dawa in Tibet. The equivalent festival in Laos is called Vixakha Bouxa and in Myanmar is called Ka-sone-la-pyae meaning Fullmoon Day of Kasone which is also the second month of the Myanmar Calendar.
The exact date of Vesak varies according to the various lunar calendars used in different traditions. In Theravada countries following the Buddhist calendar, it falls on the full moon Uposatha day (typically the 5th or 6th lunar month). In China it is the fourth month in the Chinese lunar calendar, coinciding with the first full moon of that month. The date varies from year to year in the Western Gregorian calendar but falls in April or May.
The decision to agree to celebrate Vesak as the Buddha’s birthday was formalized at the first Conference of the World Fellowship of Buddhists held in Sri Lanka in 1950, although festivals at this time in the Buddhist world are a centuries-old tradition. The Resolution that was adopted at the World Conference reads as follows:
That this Conference of the World Fellowship of Buddhists, while recording its appreciation of the gracious act of His Majesty, the Maharaja of Nepal in making the full-moon day of Vesak a Public Holiday in Nepal, earnestly requests the Heads of Governments of all countries in which large or small number of Buddhists are to be found, to take steps to make the full-moon day in the month of May a Public Holiday in honour of the Buddha, who is universally acclaimed as one of the greatest benefactors of Humanity.
On Vesak Day, Buddhists all over the world commemorate events of significance to Buddhists of all traditions: The birth, enlightenment and the passing away of Gautama Buddha. As Buddhism spread from India it was assimilated into many foreign cultures, and consequently Vesak is celebrated in many different ways all over the world.
On Vesak day, devout Buddhists and followers alike are expected and requested to assemble in their various temples before dawn for the ceremonial, and honorable, hoisting of the Buddhist flag and the singing of hymns in praise of the holy triple gem: The Buddha, The Dharma (his teachings), and The Sangha (his disciples). Devotees may bring simple offerings of flowers, candles and joss-sticks to lay at the feet of their teacher. These symbolic offerings are to remind followers that just as the beautiful flowers would wither away after a short while and the candles and joss-sticks would soon burn out, so too is life subject to decay and destruction. Devotees are enjoined to make a special effort to refrain from killing of any kind. They are encouraged to partake of vegetarian food for the day. In some countries, notably Sri Lanka, two days are set aside for the celebration of Vesak and all liquor shops and slaughter houses are closed by government decree during the two days. Also birds, insects and animals are released by the thousands in what is known as a 'symbolic act to liberation'; of giving freedom to those who are in captivity, imprisoned, or tortured against their will. Some devout Buddhists will wear a simple white dress and spend the whole day in temples with renewed determination to observe the observance of the Ten Precepts. Devout Buddhists undertake to lead a noble life according to the teaching by making daily affirmations to observe the eight Precepts. However, on special days, notably new moon and full moon days, they observe additional disciplines to train themselves to practice morality, simplicity and humility.
Some temples also display a small image of the baby Buddha in front of the altar in a small basin filled with water and decorated with flowers, allowing devotees to pour water over the statue; it is symbolic of the events following the Buddha's birth, when devas and spirits made heavenly offerings to him.
The Ten Precepts are:
Devotees are expected to listen to talks given by monks. On this day monks will recite verses uttered by the Buddha twenty-five centuries ago, to invoke peace and happiness for the Government and the people. Buddhists are reminded to live in harmony with people of other faiths and to respect the beliefs of other people as the Buddha had taught.
Vesak is celebrated as a religious and a cultural festival in Sri Lanka on the full moon of the month of May, for a duration of one week. During this week, the selling of alcohol and flesh is usually prohibited. Prisoners who are eligible for parole are often released. Celebrations include various religious and alms giving activities. Electrically lit pandols called toranas are erected in various locations in Colombo and elsewhere, most sponsored by donors, religious societies and welfare groups. Each pandol illustrates a story from the 550 Jataka Katha or the 550 Past Life Stories of the Buddha. In addition, colourful lanterns called Vesak koodu are hung along streets and in front of homes. They signify the light of the Buddha, Dhamma and the Sangha. Food stalls set up by Buddhist devotees called dansälas provide free food and drinks to passersby. Groups of people from various community organisations, businesses and government departments sing bhakti gee or Buddhist devotional songs. Colombo experiences a massive influx of public from all parts of the country during this week.
It used to be celebrated on the 8th day of the fourth month in the Chinese Lunar Calendar, based on one of the legends that proclaims the day as Buddha's birthday. At present, the celebration is observed on April 8 of the Solar Calendar since the Meiji government adopted the western solar calendar as the official calendar. Since the 8th day of the fourth month in the lunar calendar commonly falls in May of the current solar calendar, it is now celebrated about a month earlier.
In Japan, the general populace are not practicing Buddhists (and may be called casual Buddhists), so most Buddhist temples provide a way to allow the general public to celebrate and participate in only the aspect of the day being Buddha's birthday, providing the statue of baby Buddha and allowing the populace to worship or pay respect by pouring 甘茶（あまちゃ） tea made of Hydrangea. In Buddhist temples, monasteries and nunneries, more involved ceremonies are conducted for practicing Buddhists, priests, monks and nuns. Also, there are public festivals made out of the day in some areas.