Wesak Day aka Vesak Festival celebrates three major events in the life of Lord Buddha: His birth, Enlightenment and passing away (achievement of Nibbana). Lord Buddha was born as Prince Siddhattha Gotama on a full moon day in the month of Wesak (in Indian which is month of May in present day calendar) in 623 BC. Siddhattha began his search for enlightenment at age 29 and after six years realized the eternal truth, thus becoming the Buddha - which means the Awakened One. This auspicious event took place at dawn in the month of Wesak in 588 BC, which was also a full moon day. Lord Buddha taught the truth for 45 years until his final passing away into Nibbana on a full moon day in 543 BC.
Thus, all the three major events in Lord Buddha's life happened on a full moon day in the month of Wesak. As such Buddhists of both the Theravada and Mahayana tradition throughout the world celebrate this thrice-blessed day.
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.
Vesak is an annual holiday observed traditionally by practicing Buddhists in many Asian countries like Myanmar, Hong Kong, Singapore, Vietnam, Thailand, Cambodia, Laos, Malaysia, Sri Lanka, Nepal, Indonesia,Pakistan, India, and Taiwan. 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.