Nam Định is a city in the Red River Delta of northern Vietnam. It is the capital of Nam Định Province. The city of Nam Định is 90 km southeast of Vietnam's capital, Hanoi. From August 18–20 of each year, there is a festival held in Nam Định called the Cố Trạch. This celebration honors General Trần Hưng Đạo, a 13th-century national hero who led Vietnamese forces to victory over the invading Mongols.

Nam Định is a province in the southern part of the Red River Delta region of northern Vietnam. It borders Ninh Bình province to the southwest, Hà Nam province to the northwest, Thái Bình province to the northeast, and the Gulf of Tonkin to the southeast. As of 2018, it is the 52nd largest province by area and the 12th most populous province of Vietnam.