Trịnh Sâm (Vietnamese: 鄭森, 9 February 1739 – 13 September 1782) ruled northern Vietnam from 1767 to 1782 AD.

Trịnh Sâm defeated the ancient enemy of the northern state, the Nguyễn lords in the south.

The army continued south capturing more Nguyễn lands and defeating some of the forces of the Tây Sơn.

The Tây Sơn brothers were too busy fighting the Nguyễn loyalists to worry about the Trịnh in the north.

Although he was successful, this civil war fatally divided the Trịnh at a critical time when the Tây Sơn (under Nguyễn Huệ) were gaining control over the south.