Caodong school (Chinese: 曹洞宗; pinyin: Cáodòng zōng; Wade–Giles: Ts'ao-tung-tsung) is a Chinese Chan Buddhist sect, one of the Five Houses of Chán.
Some attribute the name "Cáodòng" as a union of "Dongshan" and "Caoshan" from one of his Dharma-heirs, Caoshan Benji; however, the "Cao" much more likely came from Cáoxī (曹溪), the "mountain-name" of Huineng, the Sixth Ancestor of Chan, as Caoshan was of little importance unlike his contemporary and fellow Dharma-heir, Yunju Daoying. The school emphasised sitting meditation, and later "silent illumination" techniques.
The Caodong school was founded by Dongshan Liangjie (807-869) and his Dharma-heir Caoshan Benji (840-901) (Ts'ao-shan Pen-chi, Jpn. Sōzan Honjaku). Dongshan traced back his lineage to Shitou Xiqian (700-790), a contemporary of Mazu Daoyi (709–788). Sayings to the effect that Shitou and Mazu were the two great masters of their day date from decades after their respective deaths. Shítóu's retrospective prominence owes much to the importance of Dongshan Liangjie. Shítóu does not appear to have been influential or famous during his lifetime:
He was a little-known teacher who led a reclusive life and had relatively few disciples. For decades after Shitou's death, his lineage remained an obscure provincial tradition.
In the 11th century the Caodong-school nearly extinguished.Dayang Jingxuan (942-1027), the last desecendant of the Caodong-lineage passed on his dharma-transmission via Fushan Fayuan, a teacher from the Linji school, to Fayuan's student Touzi Yiqing (1032-1083), who was born five years after Jingxuan's death.