The Chongzhen Emperor (simplified Chinese: 崇祯帝; traditional Chinese: 崇禎帝; pinyin: Chóngzhēn Dì; 6 February 1611 – 25 April 1644), personal name Zhu Youjian (Chinese: 朱由檢; pinyin: Zhū Yóujiǎn), courtesy name Deyue (德約), was the 17th and last Emperor of the Ming dynasty as well as the last ethnic Han to rule over China before the Manchu Qing conquest. He reigned from 1627 to 1644. "Chongzhen," the era name of his reign, means "honorable and auspicious."

Zhu Youjian was son of the Taichang Emperor and younger brother of the Tianqi Emperor, whom he succeeded to the throne in 1627. He battled peasant rebellions and was not able to defend the northern frontier against the Manchu. When rebels reached the capital Beijing in 1644, he committed suicide, ending the Ming dynasty. The Manchu formed the succeeding Qing dynasty.

In 1645, Zhu Yousong, who had proclaimed himself the Hongguang Emperor of the Southern Ming, gave the Chongzhen Emperor the temple name "Sizong". In historical texts, "Sizong" is the most common temple name of the Chongzhen Emperor, even though the Southern Ming rulers had changed "Sizong" to "Yizong" (毅宗) and then to "Weizong" (威宗). During the Qing dynasty, the Chongzhen Emperor's temple name was changed to "Huaizong" (懷宗).