The Double Ninth Festival (Chung Yeung Festival in Hong Kong, Vietnamese: 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 (before AD 25).

According to the I Ching, nine is a 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 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.) On this holiday some Chinese also visit the graves of their ancestors to pay their respects. People eat Chongyang Cake on the day.