Esen Taishi (Mongolian: Эсэн тайш; d. 1455) was a powerful Oirat Taishi and de facto ruler of the Northern Yuan in 15th century Mongolia . He is best known for capturing the Zhengtong Emperor of the Ming dynasty in 1450 after the Battle of Tumu Fortress and briefly reuniting the Mongols. The Four Oirat reached the peak of their power under his rule.

Esen was born to his father, Toghan, the Choros taishi (grand preceptor, from 太師) who had expanded Oirat territory substantially, with more Mongol tribes acknowledging his supremacy. As an Oirat, Esen himself was not descended from Genghis Khan, which would hamper his claim to the title of great khan throughout his life.

In his early campaigns he fought against the Chaghatayid khans of Moghulistan. Esen three times defeated and twice captured the Moghul ruler Uwais Khan (Ways Khan) (1418–1432). Esen released him out of respect for his Chinggisid blood in both cases. The third time, Uwais Khan granted Esen his sister Makhtum Khanim, who bore his two sons. Esen nominally converted to Islam in order to marry the Muslim princess, but remained effectively a shamanist.

After his father died in 1438, Esen inherited his position, taishi, for the reigning khan Taisun Khan (reigned 1433–52). Under Esen Taishi's leadership, the Mongols under Taisun Khan conquered the rest of Mongolia and received the submission of the Jurchens and Tuvans in Manchuria and Eastern Siberia. In the 1430s, Esen also took over control of the Mongol kingdom known as Kara Del in the Hami oasis between the Gobi and the Takla Makan deserts; after 1443–45 the Mongol empire reached the northern border of Korea.

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