Zhang Zai (1020–1077), also spelled Chang Tsai, courtesy name Zihou, was a Chinese philosopher during the Northern Song Dynasty (960–1127). His family originally came from Daliang (today's Kaifeng, Henan Province), and he was born in Chang'an (today's Xi'an, Shaanxi Province). He lived with his father in Hengqu Town, Meixian County (today's Meixian County, Shaanxi Province), Fengxiang Prefecture, which earned him the name Zhang Hengqu.