Onam is the biggest and the most important festival of the state of Kerala. It is a harvest festival and is celebrated with joy and enthusiasm all over the state by people of all communities. According to a popular legend, the festival is celebrated to welcome King Mahabali, whose spirit is said to visit Kerala at the time of Onam. Onam is celebrated in the beginning of the month of Chingam, the first month of Malayalam Calendar (Kollavarsham). This corresponds with the month of August-September according to Gregorian Calendar. Carnival of Onam lasts from four to ten days. First day, Atham and tenth day, Thiruonam are most important of all. Popularity and presentation of rich culture of the state during the carnival made Onam the National Festival of Kerala in 1961. Elaborate feasts, folk songs, elegant dances, energetic games, elephants, boats and flowers all are a part of the dynamic festival called Onam. Government of India has taken due notice of this vibrant and colorful festival. It promotes Onam internationally in a big way and celebrates 'Tourist Week' for Kerala during Onam celebrations. Thousands of domestic and foreign tourists visit Kerala to be a part of Onam. The Legend Story goes that during the reign of mighty asura (demon) king, Mahabali, Kerala witnessed its golden era. Every body in the state was happy and prosperous and king was highly regarded by his subjects. Apart from all his virtues, Mahabali had one shortcoming. He was egoistic. This weakness in Mahabali's character was utilized by Gods to bring an end to his reign as they felt challenged by Mahabali's growing popularity. However, for all the good deed done by Mahabali, God granted him a boon that he could annually visit his people with whom he was so attached.
It is this visit of Mahabali that is celebrated as Onam every year. People make all efforts to celebrate the festival in a grand way and impress upon their dear King that they are happy and wish him well.