Vaishakha Purnima is a Hindu celebration. Hindus believe that on this day, Lord Vishnu (protector and preserver of the universe) reincarnated in the form of Mahatma Buddha. So there is also a Buddist celebration the same day known as Vesak. See under Buddhism for details of Vesak. Both celebrations have a similar theme.

How Vaishakha Purnima is Celebrated

Temples are decorated with flowers, people bath in sacred waters and generally make donations to charity, organize blood donations, distribute gifts and food to the poor and needy as well as performing many religious rituals and activities.  

As per Hindu religion, Dharmaraj is worshipped on Vaishakha Purnima. So, a person is freed from the fear of untimely death by fasting on this day. It is believed that when Sudama, the childhood friend of Lord Krishna, reached Dwarka to meet him, Lord Krishna told him the rules (Vidhan) of Satya Vinayak Purnima Vrat. With the effect of the fast, all poverty of Sudama ended.