The founder of Buddhism, Skayamuni Buddha, was born Prince Siddhartha a full-mon day, on Apr 15 in 624 BC. Vesak Day is regarded as a time to commemorate his birth, enlightenment and passing.
The exact date of Vesak Day is determined according to the lunar calendars, but is usually falls on the day of the full moon in May.
At the 54th United Nations conference in 1999, 16 countries signed a resolution to accord international recognition to Vesak Day. The appeal to the United Nations to adopt the resolution states that "Buddha's teachings of compassion, peace and humanity have touched millions of people around the world", and millions of Buddhist followers worldwide celebrate the birth, enlightenment and passing of Buddha on Vesak Day.
In that same year, more countries including Greece, Norway, Turkey and US also sponsored the resolution.
In Dec 1999, the United Nations announced that the proposed resolution was to be adopted without voting and officially name it the "United Nations Day of Vesak".