The Double Ninth Festival (Chinese: 重九; pinyin: Chóngjiǔ , also traditional Chinese: 重陽節; pinyin: Chóngyángjié or Chung Yeung Festival in Hong Kong, Vietnamese language: Tết Trùng Cửu), observed on the ninth day of the ninth month in the Chinese calendar, is a traditional Chinese holiday, mentioned in writing since before the East Han period (thus, before AD 25).

According to the I Ching, nine is the yang number; the ninth day of the ninth lunar month (or double nine) has too much yang (a traditional Chinese spiritual concept) and is thus a potentially dangerous date. Hence, the day is also called "Double Yang Festival" (重陽節). To protect against the danger, it is customary to climb a high mountain, drink chrysanthemum wine, and wear the zhuyu (茱萸) plant, Cornus officinalis. (Both chrysanthemum and zhuyu are considered to have cleansing qualities and are used on other occasions to air out houses and cure illnesses.) Also on this holiday, some Chinese also visit the graves of their ancestors to pay their respects.

Double Ninth may have originated as a day to drive away danger, but like the Chinese New Year, over time it became a day of celebration. In contemporary times it is an occasion for hiking and chrysanthemum appreciation. Stores sell rice cakes (糕 "gāo", a homophone for height 高) inserted with mini colorful flags to represent zhuyu. Most people drink chrysanthemum tea, while a few strict traditionalists drink homemade chrysanthemum wine. Children in school learn poems about chrysanthemums, and many localities host a chrysanthemum exhibit. Mountain climbing races are also popular; winners get to wear a wreath made of zhuyu.