Tết Nguyên Đán, more commonly known by its shortened name Tết or "Vietnamese Lunar New Year", is the most important and popular holiday and festival in Vietnam. It is the Vietnamese New Year marking the arrival of spring based on the Chinese calendar, a lunisolar calendar. The name Tết Nguyên Đán is Sino-Vietnamese for Feast of the First Morning, derived from the Hán nôm characters 節 元 旦.

Tết is celebrated on the same day as Chinese New Year, though exceptions arise due to the one-hour time difference between Hanoi and Beijing resulting in the alternate calculation of the new moon. It takes place from the first day of the first month of the Lunar calendar (around late January or early February) until at least the third day. Many Vietnamese prepare for Tết by cooking special holiday foods and cleaning the house. There are a lot of customs practiced during Tết, such as visiting a person's house on the first day of the new year (xông nhà), ancestral worshipping, wishing New Year's greetings, giving lucky money to children and elderly people, and opening a shop.

Tết is also an occasion for pilgrims and family reunions. During Tết, Vietnamese visit their relatives and temples, forgetting about the troubles of the past year and hoping for a better upcoming year. They consider Tết to be the first day of spring and the festival is often called Hội xuân (spring festival).