Vesak or Wesak Day is celebrated today (3rd May) here in Malaysia and also in Sri Lanka, Laos, Cambodia and a few other countries.
Other Asian countries such as Thailand and Singapore celebrate on 1st June 2015. India, Nepal, Indonesia, Myanmar, Vietnam, Japan, Taiwan and China observe the festival on a different day.
The variation is due to the different lunar, lunisolar and Gregorian calendars used.
Buddha Day, as it is also known, commemorates the birth, enlightenment and death of Gautama Buddha.