Trịnh Căn (Hán tự:鄭 根; 18 July 1633 – 17 June 1709) ruled northern Vietnam from 1682 to 1709 (he ruled with the title Định Vương). Trịnh Căn was one of the Trịnh lords who ruled Vietnam. With the Trịnh–Nguyễn War ended, his reign was mostly devoted to administrative reforms. As far as the Lê dynasty was concerned, the emperor, Lê Hy Tông, was forced to abdicate the throne in 1706. He was replaced by Lê Du Tông.