Celebrated by various ethnic groups of Vietnamese and Chinese people, the Mid-Autumn Festival begins on the fifteenth day of the eighth month of the Chinese Han calendar. It is held on the first night of the full moon, which is a harvest moon. This purpose of this harvest festival is to gather friends and family together to give thanks for the harvest and to offer up prayers for longevity and good fortune.
The roots of the Mid-Autumn Festival can be traced back to the 16th century BCE, during the Shang Dynasty, when the indigenous peoples of China would worship the mountain gods after a successful harvest. However, it didn't really become popular until the Tang Dynasty in 618 CE when Emperor Xuanzong of Tang began to have formal proceedings of it in his personal palace.
During this holiday, it is customary for people to make and eat moon cakes, carry brightly lit lanterns and participate in numerous parlor games. It is also a time when many people engage in a form of moon worship, where offerings are made to the lunar god Chang'e. Dances are held in some countries as sort of a matchmaking ceremony to pair up single men and women.
If you are in Hong Kong during the Mid-Autumn Festival, it will be impossible not to notice mooncakes. They are believed to have originated from Yuan-dynasty （1271–1368） revolutionaries, who are said to have used the pastries to pass secret messages between each other.