Yaoshan Weiyan (Chinese: 藥山惟儼; Hànyǔ Pīnyīn: Yàoshān Wéiyǎn; Japanese: Yakusan Igen; Korean: Yaksan Yuǒm; Vietnamese: Dược Sơn Duy Nghiễm) was a Zen Buddhist monk who lived during the Tang dynasty.

The earliest biographical information comes from Tang Shen, who wrote Yaoshan's epitaph in 834, seven years after his death.

While he is traditionally regarded as a student of Shitou Xiqian, Tang Shen's inscription mentions that he stayed with Mazu Daoyi for nearly twenty years.

[1] A story involving Yaoshan is frequently referenced in the writing of Dōgen, the founder of the Sōtō school in Japan.

"According to Carl Bielefeldt, a religious studies professor at Stanford University, this passage encapsulates the essence of Dōgen's teaching on zazen.