The Nguyễn lords, also known as the Nguyễn clan, were the rulers of southern Đại Việt during the Revival Lê dynasty and ancestors of Nguyễn dynasty's emperors. The territory they ruled was known contemporarily as Đàng Trong and by Europeans as Cochinchina, in opposition to the Trịnh lords ruling northern Đại Việt, known then as Đàng Ngoài. Both Nguyễn and Trịnh lords were de jure subordinates of the Lê dynasty.

The Trịnh–Nguyễn Civil War was a 17th-century lengthy civil war waged between the two ruling families in Vietnam, the Trịnh lords of Đàng Ngoài and the Nguyễn lords of Đàng Trong, centered in today's Central Vietnam. The wars resulted in a long stalemate and century of peace before conflicts resumed in 1774 resulting in the emergence of the Tây Sơn forces following Trịnh Lords at the time, Nguyễn Lords collapsed in Saigon in 1777. During the division of Vietnam, Gianh River was used as the de facto border between two regimes Đàng Ngoài and Đàng Trong in peacetime.